Delegate Gateways and Proxy for Target Hosts in Large Layer 2 and Address Resolution with Duplicated Internet Protocol Addresses

ABSTRACT

An apparatus comprising a plurality of district boundary bridges (DBBs) in a plurality of second network districts configured to couple to a plurality of core bridges in a core network district and to a plurality of end-stations in the second network districts via a plurality of intermediate switches in the second network districts; wherein the core bridges and the DBBs are aware of a plurality of Media Access Control (MAC) addresses of the DBBs but are not aware of Internet Protocol (IP) addresses and MAC addresses of the end-stations, and wherein the IP addresses of the end-stations are mapped in a directory service (DS) in the core network district to the MAC addresses of the corresponding DBBs in the corresponding second network districts of the end-stations.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Patent Application Nos. 61/449,918 filed Mar. 7, 2011 by Linda Dunbar et al. and entitled “Directory Server Assisted Address Resolution,” 61/389,747 filed Oct. 5, 2010 by Yijun Xiong et al. and entitled “Media Access Control Address Delegation Scheme for Scalable Ethernet Networks with Duplicated Host Internet Protocol Addresses,” 61/374,514 filed Aug. 17, 2010 by Linda Dunbar et al. and entitled “Delegate Gateways and Proxy for Target hosts in Large Layer Two and Address Resolution with Duplicated Internet Protocol Addresses,” 61/359,736 filed Jun. 29, 2010 by Linda Dunbar et al. and entitled “Layer 2 to layer 2 Over Multiple Address Domains,” and 61/411,324 filed Nov. 8, 2010 by Linda Dunbar et al. and entitled “Asymmetric Network Address Encapsulation,” all of which are incorporated herein by reference as if reproduced in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Modern communications and data networks are comprised of nodes that transport data through the network. The nodes may include routers, switches, bridges, or combinations thereof that transport the individual data packets or frames through the network. Some networks may offer data services that forward data frames from one node to another node across the network without using pre-configured routes on intermediate nodes. Other networks may forward the data frames from one node to another node across the network along pre-configured or pre-established paths.

SUMMARY

In one embodiment, the disclosure includes an apparatus comprising a plurality of district boundary bridges (DBBs) in a plurality of second network districts configured to couple to a plurality of core bridges in a core network district and to a plurality of end-stations in the second network districts via a plurality of intermediate switches in the second network districts; wherein the core bridges and the DBBs are aware of a plurality of Media Access Control (MAC) addresses of the DBBs but are not aware of Internet Protocol (IP) addresses and MAC addresses of the end-stations, and wherein the IP addresses of the end-stations are mapped in a directory service (DS) in the core network district to the MAC addresses of the corresponding DBBs in the corresponding second network districts of the end-stations.

In another embodiment, the disclosure includes an apparatus comprising a plurality of edge nodes coupled to a core network, a plurality of hosts coupled to the edge nodes, wherein if multiple hosts coupled to an edge node are assigned the same duplicated address by a plurality of different customers, then the edge node is assigned a plurality of delegate addresses that correspond to the multiple hosts that are assigned the same duplicated address, and wherein the delegate addresses are used by other edge nodes and the core network to forward a plurality of frames from other hosts connected to the other edge nodes to the edge node that uses the delegate addresses to forward the frames properly to the corresponding multiple hosts that connected to the edge node and are assigned the same duplicated address.

In another embodiment, the disclosure includes a network component comprising a receiver configured to receive a plurality of IP addresses and Media Access Control (MAC) addresses for a plurality of hosts in a corresponding district in a bridged Layer 2 network, a logic circuit configured to map the IP addresses of the hosts to a MAC address, and a transmitter configured to announce the MAC address and the IP addresses of the hosts but not the MAC addresses of the hosts to a core district in the bridged Layer 2 network.

In yet another embodiment, the disclosure includes a method comprising receiving an Address Resolution Protocol (ARP) request from a first end-station in a local district in a bridged Layer 2 network for a MAC address associated with a second end-station in a second district in the bridged Layer 2 network, sending a DS query to obtain a MAC address associated with the second end-station, receiving a DS response that indicates the MAC address associated with the second end-station, and sending an ARP response that comprises the MAC address associated with the second end-station to the first end-station.

These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of Virtual Private Local Area Network (LAN) Service (VPLS) interconnected LANs.

FIG. 2 is a schematic diagram of an embodiment of a virtual Layer 2 network.

FIG. 3 is a schematic diagram of an embodiment of a border control mechanism.

FIG. 4 is a schematic diagram of an embodiment of a data frame forwarding scheme.

FIG. 5 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 6 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 7 is a schematic diagram of an embodiment of interconnected Layer 2 sites.

FIG. 8 is a schematic diagram of an embodiment of a Layer 2 extension over multiple address domains.

FIG. 9 is a schematic diagram of an embodiment of pseudo Layer 2 networks over multiple address domains.

FIG. 10 is a schematic diagram of an embodiment of a domain address restriction mechanism.

FIG. 11 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 12 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 13 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 14 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 15 is a schematic diagram of an embodiment of a broadcast scheme.

FIG. 16 is a schematic diagram of another embodiment of a broadcast scheme.

FIG. 17 is a schematic diagram of an embodiment of interconnected network districts.

FIG. 18 is a schematic diagram of another embodiment of interconnected network districts.

FIG. 19 is a schematic diagram of an embodiment of an Address Resolution Protocol (ARP) proxy scheme.

FIG. 20 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 21 is a schematic diagram of another embodiment of an ARP proxy scheme.

FIG. 22 is a schematic diagram of an embodiment of a fail-over scheme.

FIG. 23 is a schematic diagram of an embodiment of a virtual machine registration scheme.

FIG. 24 is a schematic diagram of an embodiment of location server registration and confirmation message payloads.

FIG. 25 is a schematic diagram of an embodiment of an ARP processing scheme.

FIG. 26 is a schematic diagram of an embodiment of LS query and response message payloads.

FIG. 27 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 28 is a schematic diagram of another embodiment of a data frame forwarding scheme.

FIG. 29 is a schematic diagram of an embodiment of a node failure handling scheme.

FIG. 30 is a schematic diagram of an embodiment of a link failure handling scheme.

FIG. 31 is a schematic diagram of an embodiment of a physical server.

FIG. 32 is a schematic diagram of an embodiment of an asymmetric network address encapsulation scheme.

FIG. 33 is a schematic diagram of another embodiment of an ARP processing scheme.

FIG. 34 is a schematic diagram of an embodiment of an extended ARP payload.

FIG. 35 is a schematic diagram of an embodiment of another data frame forwarding scheme.

FIG. 36 is a protocol diagram of an embodiment of an enhanced ARP processing method.

FIG. 37 is a protocol diagram of an embodiment of an extended address resolution method.

FIG. 38 is a schematic diagram of an embodiment of a network component unit.

FIG. 39 is a schematic diagram of an embodiment of a general-purpose computer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

Modern data networks, which can be Layer 2 or Layer 3 networks, provide connectivity to cloud services and virtual machines (VMs) that may need to span across multiple locations or sites. Sometimes, Layer 2 networks for data centers that connect Clusters of servers (or VMs) and storage devices have to span across multiple locations. The data center networks may also need to stay in Layer 2 level to support already deployed applications and thus save cost, e.g., in millions of dollars. Layer 2 communications between the Cluster of servers and/or storage devices include load balancing, database clustering, virtual server failure recovery, transparent operation below the network layer (Layer 3), spreading a subnet across multiple locations, and redundancy. Layer 2 communications also include a keep-alive mechanism between applications. Some applications need the same IP addresses to communicate on multiple locations, where one server may be Active and another server may be on Standby. The Active and Standby servers (in different locations) may exchange keep-alive messages between them, which may require a Layer 2 keep-alive mechanism.

FIG. 1 illustrates an embodiment of a VPLS interconnected Local Area Networks (LANs) 100. The VPLS interconnected LANs 100 is a scalable mechanism that can be used for connecting Layer 2 networks across multiple data center (DC) locations, e.g., physical locations, to establish a unified or flat Layer 2 network. The VPLS interconnected LANs 100 may comprise a VPLS 110 and a plurality of LANs 120 that may be connected to the VPLS 110 via a plurality of edge nodes 112, such as edge routers. Each LAN 120 may comprise a plurality of Layer 2 switches 122 connected to corresponding edge nodes 112, a plurality of access switches 124 connected to corresponding Layer 2 switches, a plurality of VMs 126 connected to corresponding access switches 124. The components of the VPLS interconnected LANs 100 may be arranged as shown in FIG. 1.

The VPLS 110 may be any network that is configured to connect the LANs 120 across different locations or DCs. For instance, the VPLS 110 may comprise a Layer 3 network to interconnect the LANs 120 across different DCs. The Layer 2 switches 122 may be configured to communicate at the Open System Interconnection (OSI) model data link layer. Examples of data link protocols include Ethernet for LANs, the Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), and Advanced Data Communication Control Protocol (ADCCP) for point-to-point connections. The access switches 124 may be configured to forward data between the Layer 2 switches 122 and the VMs 126. The VMs 126 may comprise system virtual machines that provide system platforms, e.g., operating systems (OSs) and/or process virtual machines that run programs or applications. The VMs 126 in each LAN 120 may be distributed over a plurality of processors, central processor units (CPUs), or computer systems. A plurality of VMs 126 in a LAN 120 may also share the same system resources, such as disk space, memory, processor, and/or other computing resources. The VMs 126 may be arranged on a shelf and connected to the corresponding LANs 120, e.g., via the access switches 124.

Some aspects of the VPLS interconnected LANs 100 may pose impractical or undesirable implementation issues. In one aspect, the VPLS 110 may require implementing a Wide Area Network (WAN) that supports Multiple Label Protocol Label Switching (MPLS). However, some operators do not support MPLS over WAN and thus may have difficulties in implementing VPLS interconnected LANs 100. Further, to resolve host link layer addresses, e.g., for the VMs 126 across the LANs 120, an IP version four (IPv4) ARP or IP version six (IPv6) Neighbor Discovery (ND) protocol may be needed, such as the IPv4 ARP described in the Internet Engineering Task Force (IETF) Request for Comments (RFC) 826 and IPv6 ND described by IETF RFC 4861, both of which are incorporated herein by reference. The ARP may flood requests to all the interconnected LANs 120 and thus exhaust a substantial amount of system resources (e.g., bandwidth). Such ARP flooding mechanism may suffer from scalability issues, as the number of LANs 120 and/or VMs 126 increases. The VPLS interconnected LANs 100 also need to setup mesh pseudo-wires (PWs) to connect to the LANs 120, which may require intensive configuration and state maintenance of tunnels. In some scenarios, the VPLS 110 may use a Border Gateway Protocol (BGP) to discover a LAN 120 and build a mesh PW for each LAN 120.

Optical Transport Virtualization (OTV) is another scalable mechanism that has been proposed for connecting Layer 2 networks across multiple locations or DCs to establish a flat Layer 2 network. OTV is a method proposed by Cisco that depends on IP encapsulation of Layer 2 communications. OTV may use an Intermediate System to Intermediate System (IS-IS) routing protocol to distribute MAC reachability within each location (e.g., DC) to other locations. The OTV scheme may also have some impractical or undesirable aspects. In one aspect, OTV may require maintaining a relatively large number of multicast groups by a provider core IP network. Since each LAN may have a separate overlay topology, there may be a relatively large quantity of overlay topologies that are maintained by the service provider IP network, which may pose a burden on the core network. OTV may also require that an edge node to use Internet Group Management Protocol (IGMP) to join different multicast groups in the IP domain. If each edge node is connected to a plurality of VLANs, the edge node may need to participate in multiple IGMP groups.

In OTV, edge devices, such as a gateway at each location, may be IP hosts that are one hop away from each other, which may not require implementing a link state protocol among the edge devices to exchange reachability information. However, the link state may also be used to authenticate a peer, which may be needed in OTV if the peer joins a VLAN by sending an IGMP version 3 (IGMPv3) report. Alternatively, OTV may use a BGP authentication method. However, the BGP authentication timing may be different than the IS-IS authentication timing. For example, BGP may be tuned for seconds performance and IS-IS may be tuned for sub-second performance. Further, the IS-IS protocol may not be suitable for handling a substantially large numbers of hosts and VMs, e.g., tens of thousands, in each location in the OTV system. OTV may also be unsuitable for supporting tens of thousands of closed user groups.

Disclosed herein are systems and methods for providing a scalable mechanism to connect a plurality of Layer 2 networks at a plurality of different locations to obtain a flat or single Layer 2 network. The scalable mechanism may resolve some of the aspects or challenges for obtaining a flat Layer 2 network that spans across multiple locations. The scalable mechanism may facilitate topology discovery across the locations by supporting scalable address resolution for applications and allowing network switches to maintain a plurality of addresses associated with all or a plurality of hosts across the locations. The scalable mechanism may also facilitate forwarding traffic across the different locations and broadcasting traffic, e.g., for unknown host addresses, and support multicast groups.

The methods include a border control mechanism to scale a relatively large flat Layer 2 over multiple locations. As such, applications, servers, and/or VMs may not be aware of a virtual Layer 2 network that comprises multiple Layer 2 networks interconnected by another network, such as a Layer 3, a Layer 2.5, or a Layer 2 network. The Layer 2 networks may be located in different or separate physical locations, multiple floors of one location, or multiple rows interconnected by Layer 3. A protocol independent address resolution mechanism may also be used and may be suitable to handle a relatively large virtual Layer 2 network and/or a substantially large number of Layer 2 networks over multiple locations.

FIG. 2 illustrates an embodiment of a virtual Layer 2 network 200 across different DC or physical locations. The virtual Layer 2 network 200 may be a scalable mechanism for connecting Layer 2 networks across multiple locations, e.g., geographical locations or DCs, or multiple sites within one data center, to establish a unified or flat Layer 2 network. The virtual Layer 2 network 200 may comprise a service network 210 and a plurality of Layer 2 networks 220 that may be connected to the service network 210 via a plurality of edge nodes 212, such as edge routers. The service network 210 may refer herein to an interconnecting network, such as a service provider network, a core network, a Layer 3 network, a Layer 2 or 2.5 network, or any other network that connects or interconnects components in multiple sites. Each Layer 2 network 220 may comprise a plurality of L2GWs 222 connected to corresponding edge nodes 212, and a plurality of intermediate switches 224 that may be connected to the L2GWs 222. The components of virtual Layer 2 network 200 may be arranged as shown in FIG. 2. The intermediate switches 224 may also be connected to a plurality of hosts and/or VMs (not shown).

The service network 210 may be any network established to interconnect the Layer 2 networks 220, such as a service provider network. For example, the service network 210 may be a Layer 2, Layer 2.5, or Layer 3 network, such as a virtual private network (VPN). The service network 210 may not be aware of all the addresses, e.g., MAC addresses, behind the L2GWs 222. The L2GWs 222 may be border nodes in each DC location and have Layer 2 interfaces to communicate internally in the DC locations. The L2GWs 222 and the intermediate switches 224 may communicate with the hosts and/or VMs in the same locations within the same Layer 2 networks 220 using the corresponding MAC addresses of the hosts. However, the L2GWs 222 and the intermediate switches 224 may not need to be aware of the MAC addresses of the hosts/VMs in the other Layer 2 networks 220. Instead, a host in one Layer 2 network 220 can use the address of a L2GW 222 of another Layer 2 network 220 (in another location or site) as the destination address to communicate with a target host in the other Layer 2 network. When a frame (e.g., an Ethernet frame) arrives at the L2GW 222 of the target site, e.g., the other Layer 2 network, the destination address of the target host may be translated by the L2GWs 222 based on the IP address carried in the payload of the frame, e.g., using a network address translation (NAT) table or a MAC address translation (MAT) table, as described below.

In an embodiment, each L2GW 222 may maintain the addresses of all the hosts/VMs within the same Layer 2 network 220 of the L2GW 222 in a local IP addresses information table (Local-IPAddrTable). The L2GW 222 may also be configured to implement a proxy ARP function, as described below. Additionally, the L2GW 222 may maintain a MAC forwarding table, which may comprise the MAC addresses for non-IP applications. The MAC addresses may comprise the MAC addresses of the hosts/VMs and the intermediate switches 224 within the same location, e.g., the same Layer 2 network 220.

The L2GW 222 may inform its peers (e.g., other L2GWs 222) in other locations (e.g., other Layer 2 networks 220) of all the active VLANs and all the IP addresses of the local hosts under each VLAN in its location. If there are non-IP applications within the domain, the L2GW 222 may also inform its peers of the MAC addresses and VLANs of those non-IP applications. A Layer 2 site or Layer 2 network 220 may have many VLANs enabled on the L2GWs′ 222 ports and the intermediate switches' 224 ports for the sake of operation convenience. Thus, a VM or host belonging to any of the enabled VLANs may be moved in without additional configuration. A VALN that is active in a site (or Layer 2 network 220) may have hosts belonging to this VLAN that resided within this site. The L2GWs 222 across the different locations may obtain the host IP addresses of all the other locations, even if the L2GWs 222 may only keep the address information for the VLANs that are active in their local sites (e.g., in a remote IP Address Information Table for each L2GW 222). If there are no hosts in the local domain that belong to VLAN identifier (VID) for the VLAN, then there may be no need to keep the remote hosts information for this VID, since there may be no communications for this VID to be targeted to local domain. The terms VLAN and VID are used herein interchangeably to refer to an established VLAN, even though a VLAN may be assigned multiple VIDs (e.g., as described in IEEE 802.1Q). Hence, each L2GW 222 may map each group of IP addresses that belongs to a location (e.g., on of the Layer 2 networks 220) to the MAC address of the corresponding L2GW 222 that belongs to the same location. The L2GW 222 also sends update of the address information to the peers when there is a change in its Local-IPAddrTable to update the information in the other peers. This may allow updating the address information and mapping in each L2GW 222 in an incremental manner.

FIG. 3 illustrates an embodiment of a border control mechanism 300. The border control mechanism 300 may be a scalable mechanism for establishing a flat or virtual Layer 2 network across multiple sites, locations or DCs. The virtual Layer 2 network may comprise a service network 310 and a plurality of Layer 2 networks 320 that may be connected to the service network 310 via a plurality of edge nodes 312, such as edge routers. Each Layer 2 network 220 may comprise a plurality of L2GWs 322 connected to corresponding edge nodes 312, and a plurality of intermediate switches 324 that may be connected to the L2GWs 322. The intermediate switches 324 may also be connected (or reachable) to hosts 326, e.g., instantiated on a VM or a server. The components of virtual Layer 2 network may be arranged as shown in FIG. 2 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Based on the border control mechanism 300, each L2GW 322 may maintain the IP addresses of hosts in all the locations belonging to the VLANs which are active in its corresponding local Layer 2 site, e.g., corresponding the Layer 2 network 320. Each L2GW 322 may also be aware of the MAC addresses of the peer L2GWs 322 in the other locations. However, the L2GW 322 may not maintain the MAC addresses of the hosts in the other locations, which may substantially reduce the size of data exchanged (and stored) among the L2GWs 322, since IP addresses may be summarized (e.g., 10.1.1.x may represent 255 hosts) while MAC addresses may not be summarized. The IP addresses maintained at the L2GW 322 may be mapped to the MAC addresses of the corresponding L2GWs 322 of the same locations. Specifically, each set of host IP addresses that belong to each location or Layer 2 network 300 may be mapped to the MAC address of the L2GW 322 in that location. However, the L2GWs 322 may exchange, across different locations, a plurality of MAC addresses for nodes that run non-IP applications.

To support address resolution across the different locations of the virtual Layer 2 network, an ARP (or ND) request may be sent from a first host 326 (host A) and be intercepted by the corresponding local L2GW 322 in a first location or Layer 2 network 320. The host A may send the ARP request to obtain the MAC address of a second host 326 (host B) in a second location or Layer 2 network 320. If the local L2GW 322 has an entry for the host B belonging to the same VLAN as host A, e.g., the IP address of the host B, the local L2GW 322 may respond to the ARP/ND request by sending its own MAC address to the host A. Alternatively, the local L2GW 322 may send the corresponding L2GW's MAC address (where host B resides) in the ARP/ND response to host A. If the local L2GW 322 does not maintain or store an entry for the host B for the VLAN, the local L2GW 322 may assume that the host B does not exist. For example, the L2GWs 322 may update their peers with their local host IP addresses and their corresponding VLAN(s) on a regular or periodic basis. It is possible that some L2GWs 322 may not have received updates for the IP addresses of newly configured hosts in other locations for some VLANs. In such case, no response is sent back and the requesting entity (host A) may send multiple ARP/ND requests for the target host.

In an embodiment, the L2GW 222 may send out a plurality of aggregated IP addresses of the local hosts under each VLAN to the other L2GW 222 in the other Layer 2 sites. The number of entries in the aggregated addresses may be substantially smaller than the corresponding number of entries in the Local-IPAddrTable of the L2GW 222. in some embodiments, the L2GW 222 may send out requests to all other L2GWs 222 in other Layer 2 sites to solicit IP addresses (in aggregated form) under a single VLAN (or any of the VLANs) in the remote sites. This may be useful when a host belonging to a VLAN that was not active is added to the local site of the L2GW 222.

Table 1 illustrates an example of mapping host addresses to the corresponding L2GW's MAC addresses and VLAN according to the border control mechanism 300. A plurality of L2GW MAC addresses (e.g., L2GW1 MAC and L2GW2 MAC) may be mapped to a plurality of corresponding host addresses. Each L2GW MAC address may be mapped to a plurality of host IP (or MAC) addresses in a plurality of VLANs (e.g., VLAN#, VLAN-x, . . . ) that may be associated with the same location or DC. Each VLAN may also comprise a plurality of virtual private groups (VPGs) (or Closed User Groups) of hosts. A VPG may be a cluster of hosts and/or VMs that belong to a Layer 2 domain (or L2 domain) and may communicate with each other via Layer 2. A Layer 2 domain may be used herein to refer to a sub-location or sub-site in a Layer 2 network. When a Layer 2 network spans across multiple sites or locations, each site may be referred to herein as a Layer 2 domain. The terms Layer 2 domain, Layer 2 site, and Layer 2 district may be used herein interchangeably. The terms domain, site, and district may also be used herein interchangeably. The hosts in the VPG may also have multicast groups established among them. The hosts/VMs within a VPG may span across multiple physical locations. Under many cases, one VLAN may be dedicated to one customer, e.g., there may be only one VPG per VLAN. As such, there may be no need to have the VPG column (or attribute) in the table under in such cases.

For example, VLAN# may comprise a plurality of hosts in multiple VPGs, including G-x1, G-x2, . . . . And each VPG may comprise a plurality of hosts. For IP applications, the hosts IP addresses in each VLAN may be mapped to the corresponding L2GW MAC address in the same location, such as in the case of VLAN# and VLAN-x. . . . ). IP Addresses may be summarized to reduce the amount of entries in the table. For non-IP applications, the hosts MAC addresses in each VLAN may be mapped to the corresponding L2GW MAC address in the same location for the VLAN, such as in the case of VLAN-x1. In some cases, there may be only one VPG for each VLAN, and hence the VPG column in Table 1 may not be needed.

TABLE 1 Border Control Mechanism L2GW VLAN VPG Host L2GW1 MAC VLAN# G-x1 All IP hosts in this group G-x2 All IP hosts in this group VLAN-x . . . G-xj VLAN-x1 G-j1 MAC (switches and/or nodes without IP addresses) MAC G-j2 MAC L2GW2 MAC

FIG. 4 illustrates an embodiment of a data frame forwarding scheme 400 that may be used in a virtual Layer 2 network across multiple locations or DCs. The virtual Layer 2 network may comprise a service network 410 and a plurality of Layer 2 networks 420 that may be connected to the service network 410 via a plurality of edge nodes 412, such as edge routers. Each Layer 2 network 420 may comprise a plurality of L2GWs 422 connected to corresponding edge nodes 412, and a plurality of intermediate switches 424 that may be connected to the L2GWs 422. The intermediate switches 424 may also be connected to hosts 426, e.g., VMs. The components of virtual Layer 2 network may be arranged as shown in FIG. 4 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Based on the data frame forwarding scheme 400, the L2GWs 422 may support the Institute of Electrical and Electronics Engineers (IEEE) 802.1ah standard for MAC-in-MAC, which is incorporated herein by reference, using an Ether Type field to indicate that an inner frame needs MAC address translation. For instance, a first L2GW 422 (GW1) may receive a frame 440, e.g., an Ethernet frame, from a first host 426 (host A) in a first location (Loc 1). The frame 440 may be intended for a second host 426 (host B) in a second location (Loc 2). The frame 440 may comprise a MAC destination address (MAC-DA) 442 for GW1 (L2GW-Loc1), a MAC source address (MAC-SA) 444 for host A (A's MAC), an IP destination address (IP-DA) 446 for host B (B), an IP source address (IP-SA) 448 for host A (A), and payload. GW1 may then add an outer MAC header to the frame 440 to obtain an inner frame 460. The outer MAC header may comprise a MAC-DA 462 for GW2 (L2GW-Loc2), a MAC-SA 464 for GW1 (L2GW-Loc1), and an Ether Type 466 that indicates that the inner frame 460 needs MAC address translation. The inner frame 460 may also comprise a MAC-DA 468 for GW1 (L2GW-Loc1) and a MAC-SA 470 for host A (A's MAC). The inner frame 460 may then be forwarded in the service network 410 to GW2, which may process the outer MAC header to translate the MAC addresses of the frame. As such, GW2 may obtain a second frame 480, which may comprise a MAC-DA 482 for host B (B's MAC), a MAC-SA 484 for host A (A's MAC), an IP-DA 486 for host B (B), an IP-SA 488 for host A (A), and payload. The second frame 480 may then be forwarded to host B in Loc 2.

The data frame forwarding scheme 400 may be simpler to implement than Cisco's OTV scheme which requires encapsulating an outer IP header. Additionally, many Ethernet chips support IEEE 802.1ah. A service instance-tag (I-TAG), such as specified in 802.1ah, may be used to differentiate between different VPGs. Thus, an I-TAG field may also be used in the data frame forwarding scheme 400 to separate between multiple VPGs of the provider domain, e.g., in the service network 410. GW2 may perform the MAC translation scheme described above using a MAT, which may be similar to using a NAT for translating a public IP into a private IP. Unlike the NAT scheme that is based on a Transmission Control Protocol (TCP) session, the MAT scheme may be based on using an inner IP address to find the MAC address.

FIG. 5 illustrates an embodiment of another data frame forwarding scheme 500 for non-IP applications. The data frame forwarding scheme 500 may use MAC addresses of non-IP hosts or hosts that implement non-IP applications instead of IP addresses to forward frames between the hosts in different locations in a virtual Layer 2 network. The virtual Layer 2 network may comprise a service network 510 and a plurality of Layer 2 networks 520 that may be connected to the service network 510 via a plurality of edge nodes 512, such as edge routers. Each Layer 2 network 520 may comprise a plurality of L2GWs 522 connected to corresponding edge nodes 512, and a plurality of intermediate switches 524 that may be connected to the L2GWs 522. The intermediate switches 524 may also be connected to hosts 526, e.g., VMs. The components of virtual Layer 2 network may be arranged as shown in FIG. 5 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Based on the data frame forwarding scheme 500, the L2GWs 522 may support IEEE 802.1ah for MAC-in-MAC. For instance, a first L2GW 520 (GW1) may receive a frame 540, e.g., an Ethernet frame, from a first host 526 (host A) in a first location (Loc 1). The frame 540 may be intended or destined for a second host 526 (host B) in a second location (Loc 2). The frame 540 may comprise a MAC-DA 542 for GW1 (L2GW-Loc1), a MAC-SA 544 for host A (A's MAC), and payload. GW1 may then add outer MAC header to the frame 540 to obtain an inner frame 560. The outer MAC header may comprise a MAC-DA 562 for GW2 (L2GW-Loc2), a MAC-SA 564 for GW1 (L2GW-Loc1), and an Ether Type 566 that indicates that the inner frame 560 is a MAC-in-MAC frame. The inner field 560 may also comprise a MAC-DA 568 for host B (B's MAC) and a MAC-SA 570 for host A (A's MAC). The inner frame 560 may then be forwarded in the service network 510 to GW2, which may process the inner frame 560 to obtain a second frame 580. The second frame 580 may comprise a MAC-DA 582 for host B (B's MAC) and a MAC-SA 584 for host A (A's MAC), and payload. The second frame 580 may then be forwarded to host B in Loc 2.

The data frame forwarding scheme 500 may be simpler to implement than Cisco's OTV scheme which requires encapsulating outer IP header. Additionally, many Ethernet chips support IEEE 802.1ah. An I-TAG, as described in 802.1ah, may be used to differentiate between different VPGs. Thus, an I-TAG field may also be used in the data frame forwarding scheme 500 to separate between multiple VPGs of the provider domain, e.g., in the service network 510. GW2 may process the second frame 580, as described above, without performing a MAC translation scheme.

FIG. 6 illustrates an embodiment of another data frame forwarding scheme 600 that may be used in a virtual Layer 2 network across multiple locations. The data frame forwarding scheme 600 may be used to forward frames from a host that moves from a previous location to a new location in the virtual Layer 2 network and maintains the same learned MAC address for a second host. The virtual Layer 2 network may comprise a service network 610 and a plurality of Layer 2 networks 620 that may be connected to the service network 610 via a plurality of edge nodes 612, such as edge routers. Each Layer 2 network 620 may comprise a plurality of L2GWs 622 connected to corresponding edge nodes 612, and a plurality of intermediate switches 624 that may be connected to the L2GWs 622. The intermediate switches 624 may also be connected to hosts 626, e.g., VMs. The components of virtual Layer 2 network may be arranged as shown in FIG. 6 and may be similar to the corresponding components of the virtual Layer 2 network 200.

When a first host 626 (host A) moves from a previous location (Loc 1) to a new location (Loc 3), host A may still use the same learned MAC address for a second host 626 (host B). According to the data frame forwarding scheme 600, a L2GW 622 of Loc 3 (GW3) may support 802.1ah MAC-in-MAC using an Ether Type field to indicate that an inner frame needs MAC address translation. GW3 may implement a data frame forwarding scheme similar to the data frame forwarding scheme 400 to send data to a second L2GW 622 of Loc 2 (GW2) using GW2's MAC address in an outer MAC header. Thus, GW2 may decapsulate the outer MAC header and perform MAC address translation, as described above (for the data frame forwarding scheme 400).

For instance, GW3 may receive a frame 640, e.g., an Ethernet frame, from host A after moving to Loc 3. The frame 640 may be intended for host B in Loc 2. The frame 640 may comprise a MAC-DA 642 for a previous L2GW 622 (GW1) of Loc 1 (L2GW-Loc1), a MAC-SA 644 for host A (A's MAC), an IP-DA 646 for host B (B), an IP-SA 648 for host A (A), and payload. GW3 may then add an outer MAC header to the frame 640 to obtain an inner frame 660. The outer MAC header may comprise a MAC-DA 662 for GW2 (L2GW-Loc2), a MAC-SA 664 for GW1 (L2GW-Loc1), and an Ether Type 666 that indicates that the inner frame 660 needs MAC address translation. The inner frame 660 may also comprise a MAC-DA 668 for host B (B's MAC) and a MAC-SA 670 for host A (A's MAC). The inner frame 660 may then be forwarded in the service network 610 to GW2, which may process the outer MAC header to translate the MAC addresses of the frame. As such, GW2 may obtain a second frame 680, which may comprise a MAC-DA 682 for host B (B's MAC), a MAC-SA 684 for host A (A's MAC), and payload. The second frame 680 may then be forwarded to host B in Loc 2.

Further, host B may move from Loc 2 to another location, e.g., Loc 4 (not shown). If GW2 has learned that host B has moved from Loc 2 to Loc 4, then GW2 may use the MAC address of another L2GW 622 in Loc 4 (GW4) as a MAC-DA in an outer MAC header, as described above. If GW2 has not learned that host B has moved from Loc 2 to Loc 4, then the frame may be forwarded by GW2 without the outer MAC header. As such, the frame may be lost, e.g., in the service network 610. The frame may be lost temporarily until the frame is resent by GW2 after host B announces its new location to GW2 or Loc 2.

FIG. 7 illustrates an embodiment of interconnected Layer 2 sites (or districts) 700 that may implement a similar border control mechanism as the virtual Layer 2 networks above. The interconnected Layer 2 sites 700 may comprise a plurality of L2GWs 722 connected by a plurality of border or edge nodes 712. The edge nodes, e.g., edge routers, may belong to a service network, e.g., a Layer 3 network. The interconnected Layer 2 sites 700 may also comprise a plurality of intermediate switches 724 connected to the L2GWs 722, and a plurality of VMs 726 connected to the intermediate switches 724. The L2GWs 722, intermediate switches 724, and VMs 726 may support multiple subsets that correspond to a plurality of Layer 2 (L2) address domains. The components of the interconnected Layer 2 sites 700 may be arranged as shown in FIG. 7 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Each L2 address domain may use a border control mechanism, such as the border control mechanism 300, where the intermediate switches 724 and VMs 726 within each Layer 2 domain may be aware of local MAC addresses but not the MAC addresses and VLAN for hosts, servers, and/or VMs 726 in the other L2 address domains. However, the hosts, servers, and/or VMs 726 may communicate with each other as in a single flat Layer 2 network without being aware of the different Layer 2 domains. The Layer 2 domains may be interconnected to each other via the border or edge nodes 712, which may be interconnected over a core network or service provider network (not shown). The L2 address domains may be located in one DC site or at a plurality of geographic sites. The architecture of the interconnected Layer 2 sites 700 across the multiple sites (locations) may also be referred to herein as a Layer 2 extension over multiple sites interconnected by a service network (Layer 3, 2.5, 2 or other networks), pseudo Layer 2 networks over sites interconnected by a service network, virtual Layer 2, or pseudo Layer 2 networks.

FIG. 8 illustrates one embodiment of a Layer 2 extension 800 over multiple sites interconnected by a service network. The Layer 2 extension 800 may comprise a plurality of L2GWs 822 connected to a plurality of border or edge nodes 812, which may belong to a service provider or core network (not shown). The Layer 2 extension 800 may also comprise a plurality of intermediate switches 824 connected to the L2GWs 822, and a plurality of hosts/servers/VMs 826 connected to the intermediate switches 824. The intermediate switches 824 and hosts/servers/VMs 826 may be separated or arranged into a plurality of L2 address domains. For example, one of the L2 sites is indicated by the dashed line circle in FIG. 8. The L2GWs 822, intermediate switches 824, and hosts/servers/VMs 826 may correspond to a Layer 2 network at one or multiple DC locations. The components of the Layer 2 extension 800 may be arranged as shown in FIG. 8 and may be similar to the corresponding components of the virtual Layer 2 network 200.

FIG. 9 is a schematic diagram of an embodiment of pseudo Layer 2 networks 900 over multiple locations. The pseudo Layer 2 networks 900 may be a mechanism for connecting Layer 2 across multiple locations, e.g., geographical locations or DCs, to establish one flat Layer 2 network. The pseudo Layer 2 networks 900 may comprise a service provider or core network 910 and a plurality of Layer 2 network domains 920 that may be connected to the service provider or core network 910 via a plurality of edge nodes 912, such as edge routers. Each Layer 2 site 920 may be located at a different DC site (or floor, or zone) or location and may comprise a plurality of L2GWs 922 connected to corresponding edge nodes 912, and a plurality of intermediate switches 924 connected to corresponding L2GWs 922. The intermediate switches 924 may also be connected to a plurality of hosts/servers/VMs (not shown). The components of the pseudo Layer 2 networks 900 may be arranged as shown in FIG. 9 and may be similar to the corresponding components of the virtual Layer 2 network 200.

FIG. 10 illustrates an embodiment of a domain address restriction mechanism 1000. The domain address restriction mechanism 1000 may be used in pseudo Layer 2 networks over multiple sites to handle address resolution between the different Layer 2 sites. The pseudo Layer 2 networks over multiple sites may comprise a service network 1010 and a plurality of Layer 2 network sites 1020 that may be connected to the service network 1010 via a plurality of edge nodes 1012. The Layer 2 sites 1020 may be located at the same or different DC sites and may comprise a plurality of L2GWs 1022 connected to corresponding edge nodes 1012, and a plurality of intermediate switches 1024 connected to corresponding L2GWs 1022. The intermediate switches 1024 may also be connected to a plurality of hosts/servers/VMs 1026. The components of the pseudo Layer 2 networks may be arranged as shown in FIG. 10 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Specifically, a MAC address of a L2GW 1022 in one Layer 2 site 1020 may be used as a proxy for all or a plurality of the hosts outside this local site. In a first option (option 1), a MAC address for a local L2GW 1022 in the Layer 2 sites 1020 may be used as the proxy for hosts in the other Layer 2 network sites 1020. In this scenario, only addresses of local hosts may be learned by the intermediate switches 1024 and hosts/servers/VMs 1026 in the same local Layer 2 sites 1020. The MAC addresses of external L2GWs 1022 in other Layer 2 sites 1020 may not be exposed to the local Layer 2 sites 1020.

Alternatively, in a second option (option 2), the MAC addresses of L2GWs 1022 in a remote Layer 2 site 1020 may be used as a proxy for all hosts residing in the corresponding site. Under this option, the MAC addresses of external L2GWs 1022 in other Layer 2 sites 1020 may be learned in each Layer 2 site 1020. In this option, the MAC addresses of remote L2GWs 1022 that correspond to the Layer 2 site 1020, where a target host resides, may be returned in response to local host's ARP/ND requests, e.g., when a host intends to communicate with an host in an remote Layer 2 site 1020 and requests the address of the external host. Option 2 may have some advantages over option 1 in some situations.

According to the domain address restriction mechanism 1000, each L2GW 1022 may be aware of all the hosts addresses in the same local Layer 2 site 1020 of the L2GW 1022, e.g., using a reverse ARP scheme or other methods. Each L2GW 1022 may also inform other L2GWs 1022 in other Layer 2 sites 1020 of the hosts IP addresses and the corresponding VLANs (or VIDs).

To resolve addresses within one Layer 2 across the different sites, an ARP/ND request may be sent from a first host 1026 (host A) to a corresponding local L2GW 1022 in a first site (Site 1). The host A may send the ARP/ND request to obtain the MAC address of a second host 1026 (host B) in a second site (Site 2). If the local L2GW 1022 has an entry for the host B for the VLAN, e.g., the IP address of the host B under the same VLAN, the local L2GW 1022 may respond to the ARP request by sending its own MAC address (option 1) or the MAC address of a second L2GW 1022 associated with host B in Site 2 (option 2) to the host A. The ARP/ND request sent from one site, e.g., Site 1, may be intercepted by local L2GW 1022, and may not be forwarded (by the local L2GW 1022) to another site. If the local L2GW 1022 does not comprise an entry for host B under the same VLAN, the local L2GW 1022 may assume that host B does not exist and may not send a response to host A. The L2GWs 1022 of each site may send updates of their local hosts' IP addresses and their corresponding VLAN on a regular or periodic basis to their peer L2GWs 1022. It is possible that some L2GWs 1022 may not have received the IP addresses of newly configured hosts in other locations. Typically, host A may send ARP/ND request repetitively if no response is received.

FIG. 11 illustrates an embodiment of a data frame forwarding scheme 1100 that may be used to forward messages or frames within one pseudo Layer 2 networks over multiple sites. The pseudo Layer 2 network over multiple sites may comprise a service provider or core network 1110 and a plurality of Layer 2 network domains 1120 that may be connected by the service provider or core network 1110 via a plurality of edge nodes 1112. The Layer 2 network domains 1120 may be located at one or more DC sites or locations and may comprise a plurality of L2GWs 1122 connected to corresponding edge nodes 1112, and a plurality of intermediate switches 1124 connected to corresponding L2GWs 1122. The intermediate switches 1124 may also be connected to a plurality of hosts/servers/VMs 1126. The components of the pseudo Layer 2 networks may be arranged as shown in FIG. 11 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Based on the data frame forwarding scheme 1100, a first L2GW 1022 (GW1) may receive a first frame 1140, e.g., an Ethernet frame, from a first host 1126 (host A) in a first address domain 1120 (domain 1). The first frame 1140 may be intended for a second host 1126 (host B) in a second address domain 1120 (domain 2). The first frame 1140 may comprise a MAC-DA 1142 for a L2GW 1122 (GW). Host A may obtain the MAC address of GW in an ARP response from GW1 in return to an ARP request for host B. GW may correspond to GW1 in domain 1 (according to option 1) or to a second L2GW 1122 (GW2) in domain 2 (according to option 2). The first frame 1140 may also comprise a MAC-SA 1144 for host A (A's MAC), an IP-DA 1146 for host B (B), an IP-SA 1148 for host A (A), and payload.

Based on option 1, GW1 may receive the first frame 1140, look up the VID/destination IP address of host B (e.g., as indicated by IP-DA 1146 for host B), and replace the MAC-DA 1142 for GW in the first frame 1140 with a MAC-DA 1162 for GW2 in an inner frame 1160. GW1 may also replace the MAC-SA 1144 for host A (A's MAC) in the first frame 1140 with a MAC-SA 1164 for GW1 in the inner frame 1160. The inner frame 1160 may also comprise an IP-DA 1166 for host B (B), an IP-SA 1168 for host A (A), and payload. GW1 may send the inner frame 1160 to domain 2 via the service provider or core network 1110. Based on option 2, GW1 may filter out all data frames intended for GW2 or any other external L2GW 1122, for instance based on an access list, replace the source addresses of the data frames (MAC-SA 1144 for host A or A's MAC) with GW1's own MAC address, and then forward the data frames based on the destination MAC.

GW2 may receive the inner frame 1160 and process the inner frame 1160 to translate the MAC addresses of the frame. Based on option 1, GW2 may receive the inner frame 1160, look up the VID/destination IP address of host B (e.g., as indicated by IP-DA 1166 for host B), and replace the MAC-DA 1162 for GW2 in the inner frame 1160 with a MAC-DA 1182 for host B (B's MAC) in a second frame 1180. GW2 may also replace the MAC-SA 1164 for GW1 in the inner frame 1160 with a MAC-SA 1184 for GW2 in the second frame 1180. The second frame 1180 may also comprise an IP-DA 1186 for host B (B), an IP-SA 1188 for host A (A), and payload. GW2 may then send the second frame 1180 to the destination host B. Based on option 2, GW2 may only look up the VID/destination IP address of host B (e.g., as indicated by IP-DA 1166 for host B), and replace the MAC-DA 1162 for GW2 with a MAC-DA 1182 for host B (B's MAC) in the second frame 1180. However, GW2 may keep the MAC-SA 1164 for.

As described above, GW2 may perform MAC address translation using the IP-DA 1166 for host B in the inner frame 1160 to find a corresponding MAC-DA 1182 for host B (B's MAC) in a second frame 1180. This MAC translation step may require about the same amount of work as a NAT scheme, e.g., for translating public IP address to private IP address. The MAC address translation in the data frame forwarding scheme 1100 may be based on using the host IP address to find the corresponding MAC address, while the NAT scheme is based on a TCP session.

FIG. 12 illustrates an embodiment of another data frame forwarding scheme 1200 that may be used to forward messages or frames between pseudo Layer 2 networks over multiple address domains. Specifically, the pseudo Layer 2 networks may be interconnected via an IP/MPLS network. The pseudo Layer 2 networks over the address domains may comprise an IP/MPLS network 1210 and a plurality of Layer 2 network domains 1220 that may be connected to the IP/MPLS network 1210 via a plurality of edge nodes 1212. The IP/MPLS network 210 may provide an IP service to support an inter domain between the address domains, e.g., the Layer 2 network domains 1220. The Layer 2 network domains 1220 may be located at one or more DC sites or locations and may comprise a plurality of L2GWs 1222 connected to corresponding edge nodes 1212, and a plurality of intermediate switches 1224 connected to corresponding L2GWs 1222. The intermediate switches 1224 may also be connected to a plurality of hosts/servers/VMs 1226. The components of the pseudo Layer 2 networks may be arranged as shown in FIG. 12 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Based on the data frame forwarding scheme 1200, a first L2GW 1022 (GW1) may receive a first frame 1240, e.g., an Ethernet frame, from a first host 1226 (host A) in a first address domain (domain 1). The first frame 1240 may be intended for a second host 1226 (host B) in a second address domain (domain 2). The first frame 1240 may comprise a MAC-DA 1242 for a L2GW 1222 (GW). Host A may obtain the MAC address of GW in an ARP response from GW1 in return to an ARP request for host B. GW may correspond to GW1 in domain 1 (according to option 1) or to a second L2GW 1222 (or GW2) in domain 2 (according to option 2). The first frame 1240 may also comprise a MAC-SA 1244 for host A (A's MAC), an IP-DA 1246 for host B (B), an IP-SA 1248 for host A (A), and payload.

GW1 may receive the first frame 1240 and process the frame based one of two options. In a first option, GW1 may receive the first frame 1240 and add an IP header to obtain an inner frame 1250. The IP header may comprise an IP-DA 1251 for GW2 and an IP-SA 1252 for GW1. GW1 may also process the first frame 1240 similar to the data frame forwarding scheme 1100 to obtain in the inner frame 1250 a MAC-DA 1253 for GW2, a MAC-SA 1254 for GW1, an IP-DA 1256 for host B (B), and an IP-SA 1257 for host (A). GW1 may send the inner frame 1250 to GW2 via the IP/MPLS network 1210. GW2 may receive the inner frame 1250 and process the inner frame 1250 similar to the data frame forwarding scheme 1100 to obtain a second frame 1280 that comprises a MAC-DA 1282 for host B (B's MAC), a MAC-SA 1284 for GW1 (according to option 1) or GW2 (according to options 2), an IP-DA 1286 for host B (B), an IP-SA 1288 for host A (A), and payload. GW2 may then forward the second frame 1250 to host B.

In a second option, GW1 may receive the first frame 1240 and replace the MAC-DA 1242 for GW in the first frame 1240 with an IP-DA 1262 for GW2 in an inner frame 1260. GW1 may also replace the MAC-SA 1244 for host A (A's MAC) in the first frame 1240 with an IP-SA 1264 for GW1 in the inner frame 1260. The inner frame 1260 may also comprise an IP-DA 1266 for host B (B), an IP-SA 1268 for host A (A), and payload. GW1 may send the inner frame 1260 to GW2 via the IP/MPLS network 1210. GW2 may receive the inner frame 1260 and replace the IP-DA 1162 for GW2 in the inner frame 1260 with a MAC-DA 1282 for host B (B's MAC) in a second frame 1280. GW2 may also replace the IP-SA 1264 for GW1 in the inner frame 1260 with a MAC-SA 1284 for GW2 (according to option 1) or GW1 (according to options 2) in the second frame 1280. The second frame 1280 may also comprise an IP-DA 1286 for host B (B), an IP-SA 1288 for host A (A), and payload. GW2 may then forward the second frame 1250 to host B.

In the above pseudo Layer 2 extension or networks across multiple domains, each L2GW may be configured for IP-MAC mapping of all the hosts in each VLAN in the L2GW's corresponding address domain. Each L2GW may also send IP addresses of all the hosts in each VLAN in the corresponding address domain to other L2GWs in other address domains on a regular or periodic basis. Thus, the L2GWs in the address domains may obtain IP addresses of hosts under each VLAN for all the address domains of the pseudo Layer 2 network. The MAC addresses of the hosts in each address domain may not be sent by the local L2GW to the L2GWs of the other address domains, which may substantially reduce the size of data exchanged between the L2GWs. However, the L2GWs of different address domains may exchange among them the MAC addresses corresponding to non-IP applications, e.g., if the number of non-IP applications is relatively small. A BGP or similar method may be used to exchange the address information, including updates, between the L2GWs across the address domains.

Table 2 illustrates an example of mapping host addresses to the corresponding L2GW's MAC addresses in pseudo Layer 2 networks. A plurality of L2GW MAC addresses (e.g., GW-A MAC and GW-B MAC) may be mapped to a plurality of corresponding host addresses. Each L2GW MAC address may be mapped to a plurality of host IP (or MAC) addresses in a plurality of VLANs (e.g., VID-1, VID-2, VID-n, . . . ), which may be in the same address domain.

TABLE 2 IP-MAC Mapping L2GW VLAN Host GW-A MAC VID-1 IP addresses of all hosts in this VLAN (IP Prefix) MAC addresses (non-IP applications) VID-2 IP addresses of all hosts in this VLAN (IP Prefix) MAC addresses (non-IP applications) VID-n IP addresses of all hosts in this VLAN (IP Prefix) MAC addresses (non-IP applications) GW-B MAC

The pseudo Layer 2 extension or networks schemes above may restrict the MAC addresses of an address domain from being learned by any switches/servers/VMs in another address domain. The schemes may also provide a scalable mechanism to connect substantially large Layer 2 networks in multiple locations. In relatively large Layer 2 networks that span across multiple address domains, the schemes may limit the number of MAC addresses that may be learned by any switch in the pseudo Layer 2 networks, where each switch may only learn the MAC addresses of the local address domain of the switch. The scheme may also provide reachability discovery across multiple address domains using scalable address resolution across the address domains. Additionally, the schemes may facilitate forwarding between address domains and the broadcast for unknown addresses, and support multicast groups.

FIG. 13 illustrates an embodiment of another data frame forwarding scheme 1300 that may be used to forward messages or frames between pseudo Layer 2 networks over multiple address domains and locations. The data frame forwarding scheme 1300 may be based on option 1 described above and may be used to forward frames from a host that moves from a previous location to a new location in the pseudo Layer 2 networks and maintains the same learned MAC address for a second host. The pseudo Layer 2 networks may comprise a service provider or core network 1310 and a plurality of Layer 2 network domains 1320 that may be connected to the service provider or core network 1310 via a plurality of edge nodes 1112. The Layer 2 network domains 1320 may be located at multiple DC sites or locations and may comprise a plurality of L2GWs 1322 connected to corresponding edge nodes 1312, and a plurality of intermediate switches 1324 connected to corresponding L2GWs 1322. The intermediate switches 1324 may also be connected to a plurality of hosts/servers/VMs 1326. The components of the pseudo Layer 2 networks may be arranged as shown in FIG. 13 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Based on the data frame forwarding scheme 1300, GW3 may receive a first frame 1340, e.g., an Ethernet frame, from a first host 1326 (host A) after moving from Loc 1 to Loc 3. The frame 1340 may be intended for a second host 1326 (host B) in Loc 2. The first frame 1340 may comprise a MAC-DA 1342 for GW1 in Loc 1, a MAC-SA 1344 for host A (A's MAC), an IP-DA 1346 for host B (B), an IP-SA 1348 for host A (A), and payload. GW3 may process the first frame 1340 and replace the MAC-SA 1344 for host A (A's MAC) in the first frame 1340 with a MAC-SA 1354 for GW3 in a first inner frame 1350, e.g., similar to the data frame forwarding scheme 1100. The first inner frame 1350 may also comprise a MAC-DA 1352 for GW1, an IP-DA 1356 for host B (B), an IP-SA 1358 for host A (A), and payload. GW3 may send the first inner frame 1350 to Loc 1 via the service provider or core network 1310.

GW1 may receive the first inner frame 1350, look up the VID/destination IP address of host B (e.g., as indicated by IP-DA 1356 for host B), and replace the MAC-DA 1352 for GW1 in the first frame 1340 with a MAC-DA 1362 for GW2 in a second inner frame 1360. The second inner frame 1360 may also comprise a MAC-SA 1364 for GW3, an IP-DA 1366 for host B (B), an IP-SA 1368 for host A (A), and payload. GW1 may send the second inner frame 1360 to Loc 2 via the service provider or core network 1310.

GW2 may receive the second inner frame 1360 and process the second inner frame 1360 to translate the MAC addresses of the frame. GW2 may receive the second inner frame 1360, look up the VID/destination IP address of host B (e.g., as indicated by IP-DA 1366 for host B), and replace the MAC-DA 1362 for GW2 in the inner frame 1360 with a MAC-DA 1382 for host B (B's MAC) in a second frame 1380. GW2 may also replace the MAC-SA 1364 for GW3 in the second inner frame 1360 with a MAC-SA 1384 for GW2. GW2 may then send the second frame 1380 to the destination host B.

Further, host B may move from Loc 2 to another location, e.g., Loc 4 (not shown). If GW2 has learned that host B has moved from Loc 2 to Loc 4, then GW2 may send updates to its peers (other L2GWs 1322 in other locations). When a L2GW 1322 in Loc 4 (GW4) learns that host B is added to its domain, GW4 may also update its peers. As such, each L2GW 1322 may have updated address information about host B. If a L2GW 1322 has not learned that host B has moved from Loc 2 to Loc 4, then the L2GW 1322 may still send a frame intended for host B from local hosts to Loc 2. In turn, GW2 may receive and forward the frame in Loc 2, where the frame is lost since host B has moved from Loc 2. The frame may be lost temporarily until the frame is resent by the L2GW 1322 after host B announces its new location to the L2GW 1322.

FIG. 14 illustrates an embodiment of another data frame forwarding scheme 1400 that may be used to forward messages or frames between pseudo Layer 2 networks over multiple sites or domains. The data frame forwarding scheme 1400 may be based on option 2 described above and may be used to forward frames from a host that moves from a previous location to a new location in the pseudo Layer 2 networks and maintains the same learned MAC address for a second host. The pseudo Layer 2 networks may comprise a service network 1410 and a plurality of Layer 2 network domains 1420 that may be connected by the service network 1410 via a plurality of edge nodes 1412. The Layer 2 network domains 1420 may be located at multiple DC sites or locations and may comprise a plurality of L2GWs 1422 connected to corresponding edge nodes 1412, and a plurality of intermediate switches 1424 connected (directly or indirectly) to corresponding L2GWs 1422. The intermediate switches 1424 may also be connected (directly or indirectly) to a plurality of hosts/servers/VMs 1426. The components of the pseudo Layer 2 networks may be arranged as shown in FIG. 14 and may be similar to the corresponding components of the virtual Layer 2 network 200.

Based on the data frame forwarding scheme 1400, GW3 may receive a first frame 1440, e.g., an Ethernet frame, from a first host 1426 (host A) after moving from Loc 1 to Loc 3. The frame 1440 may be intended for a second host 1426 (host B) in Loc 2. The first frame 1340 may comprise a MAC-DA 1442 for GW2 in Loc 2, a MAC-SA 1444 for host A (A's MAC), an IP-DA 1446 for host B (B), an IP-SA 1448 for host A (A), and payload. GW3 may process the first frame 1440 and replace the MAC-SA 1444 for host A (A's MAC) in the first frame 1440 with a MAC-SA 1464 for GW3 in an inner frame 1460, e.g., similar to the data frame forwarding scheme 1100. The inner frame 1460 may also comprise a MAC-DA 1462 for GW2, an IP-DA 1466 for host B (B), an IP-SA 1468 for host A (A), and payload. GW3 may send the inner frame 1460 to Loc 2 via the service provider or core network 1410.

GW2 may receive the inner frame 1460 and process the inner frame 1460 to translate the MAC addresses of the frame. GW2 may receive the inner frame 1460, look up the VID/destination IP address of host B (e.g., as indicated by IP-DA 1466 for host B), and replace the MAC-DA 1462 for GW2 in the inner frame 1460 with a MAC-DA 1482 for host B (B's MAC) in a second frame 1480. The inner frame 1460 may also a MAC-SA 1484 for GW3. GW2 may then send the second frame 1480 to the destination host B.

Further, host B may move from Loc 2 to another location, e.g., Loc 4 (not shown). If GW2 has learned that host B has moved from Loc 2 to Loc 4, then GW2 may send updates to its peers (other L2GWs 1322 in other locations). When a L2GW 1322 in Loc 4 (GW4) learns that host B is added to its domain, GW4 may also update its peers. As such, each L2GW 1322 may have updated address information about host B. If a L2GW 13222 has not learned that host B has moved from Loc 2 to Loc 4, then the L2GW 1322 may still send a frame intended for host B from local hosts to Loc 2. In turn, GW2 may receive and forward the frame in Loc 2, where the frame is lost since host B has moved from Loc 2. The frame may be lost temporarily until the frame is resent by the L2GW 1322 after host B announces its new location to the L2GW 1322.

The pseudo Layer 2 extension or networks described above may support address resolution in each address domain and may use a mechanism to keep the L2GWs currently updated with IP addresses of all the hosts in their domains/locations. Address resolution and IP address updating may be implemented in one of two scenarios. The first scenario corresponds to when a host or VM is configured to send gratuitous ARP messages upon being added or after moving to a network. The second scenario corresponds to when a host or VM that is added to or has moved to a network does not send ARP announcements. The two scenarios may be handled as described in the virtual Layer 2 networks above.

The virtual Layer 2 networks and similarly the pseudo Layer 2 networks described above may support address resolution in each location/domain and a mechanism to keep each L2GW currently updated with IP addresses of its local hosts in its location/domain. In one scenario, when a host or a VM is added to the network, the host or VM may send an ARP announcement, such as a gratuitous ARP message, to its Layer 2 network or local area. In another scenario, the host or VM added to the network may not send an ARP announcement.

In the first scenario, a new VM in a Layer 2 network or location/domain may send a gratuitous ARP message to a L2GW. When the L2GW receives the gratuitous ARP message, the L2GW may update its local IPAddrTable but may not forward the gratuitous ARP message to other locations/domains or Layer 2 networks. Additionally, the L2GW may use a timer for each entry in the IPAddrTable to handle the case of shutting down or removing a host from a location/domain. If the timer of an entry is about to expire, the L2GW may send an ARP (e.g., via uni-cast) to the host of the entry. Sending the ARP as a uni-cast message instead of broadcasting the ARP may avoid flooding the local Layer 2 domain of the host and the L2GW. When a host moves from a first location to a second location, a L2GW may receive an update message from the first location and/or the second location. If the L2GW detects that the host exists in both the first location and the second location, the L2GW may send a local ARP message in the first location to verify that the host does not exist anymore in the first location. Upon determining that the host is no longer present in the first location, for example if not response to the ARP message is detected, the L2GW may update its local IPAddrTable accordingly. If the L2GW receives a response for the ARP message for its own location, then a MAC multi-homing mechanism of BGP may be used.

In the second scenario, the new host in a location may not send an ARP announcement. In this case, when an application (e.g., at a host) needs to resolve the MAC address for an IP host, the application may send out an ARP request that may be broadcasted in the location. The ARP request may be intercepted by a L2GW (or a Top-of-Rack (ToR) switch), e.g., by implementing a proxy ARP function. In a relatively large DC, the L2GW may not be able to process all the ARP requests. Instead, a plurality of L2GW delegates (e.g., ToR switches) may intercept the ARP announcements. The L2GW may push down the IP addresses (e.g., a summary of IP addresses) that are learned from other locations to its corresponding delegates (ToR switches). The delegates may then intercept the ARP requests from hosts or local servers. If an IP address in the ARP request from a host or server is present in the IPAddrTable of the L2GW, the L2GW may return an ARP response with the L2GW's MAC address to the host or server, without forwarding the broadcasted ARP request any further. For non-IP applications, e.g., applications that run directly over Ethernet without IP, the applications may use MAC addresses as DAs when sending data. The non-IP applications may not send an ARP message prior to sending the data frames. The data frames may be forwarded using unknown flooding or Multiple MAC registration Protocol (MMRP).

In one scenario, an application (e.g., on a host) may send a gratuitous ARP message upon joining one of the interconnected Layer 2 networks in one location to obtain a MAC address for a targeted IP address. When the L2GW or its delegate (e.g., ToR switch) may receive the ARP request and check its IP host table. If the IP address is found in the table, the L2GW may send an ARP reply to the application. The L2GW may send its MAC address in the reply if the targeted IP address corresponds to an IP host in another location. If the IP address is not found, no reply may be sent from the L2GW, which may maintain the current or last updated IP addresses of the hosts in all locations. In relatively large DCs, multiple L2GWs may be used, e.g., in the same location, where each L2GW may handle a subset of VLANs. As such, each L2GW may need to maintain a subset of IP addresses that comprise the IP addresses of the hosts in the corresponding VLAN.

In the case of substantially large DCs, e.g., that comprise tens of thousands of VMs, it may be difficult for a single node to handle all the ARP requests and/or gratuitous ARP messages. In this case, several schemes may be considered. For instance, a plurality of nodes or L2GWs may be used to handle different subsets of VLANs within a DC, as described above. Additionally or alternatively, multiple delegates may be assigned for a L2GW in each location. For instance, a plurality of ToR switches or access switches may be used. Each L2GW's delegate may be responsible for intercepting gratuitous ARP messages on its corresponding downlinks or in the form of a Port Binding Protocol. The delegates may send a consolidated address list (AddressList) to their L2GWs. The L2GW may also push down its learned IP address lists from other locations to its delegates. If there are multiple L2GWs in a location that are responsible for different subsets of VLANS, the delegates may need to send a plurality of consolidated messages that comprise each the AddressLists in the VLANs associated with the corresponding L2GWs.

In comparison to Cisco's OTV scheme, using the virtual Layer 2 network described above may substantially reduce the size of forwarding tables on intermediate switches in each location. The switches in one location may not need to learn MAC addresses of IP hosts in other locations, e.g., assuming that the majority of hosts run IP applications. This scheme may also substantially reduce the size of the address information exchanged among the L2GWs. For example, a subnet that may comprise thousands of VMs may be mapped to a L2GW MAC address. The hierarchical Layer 2 scheme of the virtual Layer 2 network may use 802.1ah standard, which may be supported by commercial Ethernet chip sets, while Cisco's scheme uses proprietary IP encapsulation. Both schemes may use peer location gateway device (L2GW) address as outer destination address. The hierarchical Layer 2 scheme may also use address translation, which may be supported by current IP gateways. However, the hierarchical Layer 2 scheme may use MAC address translation instead of IP address translation. The MAC address translation may need carrier grade NAT implementation that can perform address translation for tens of thousands of addresses.

In an embodiment, a VLAN may span across multiple locations. Thus, a multicast group may also span across multiple locations. Specifically, the multicast group may span across a subset of locations in the virtual Layer 2 network. For example, if there are about ten locations in the virtual Layer 2 network, the multicast group may only span across three of the ten locations. A multicast group within one service instance may be configured by a network administrator system (NMS) or may be automatically established in Layer 2 using MMRP. Since L2GW supports 802.1ah, the L2GW may have a built-in component to map client multicast groups to proper multicast groups in the core network. In a worst case scenario, the L2GW may replicate the multicast data frames to all the locations of the service instance. For example, according to Microsoft research data, about one out of four traffic may go to a different location. Thus, the replication by L2GW may be simpler than implementing a complicated mechanism in the Provider core.

The virtual Layer 2 network may support broadcast traffic, such as for ARP requests and/or Dynamic Host Configuration Protocol (DHCP) requests. The broadcast traffic may be supported by creating multiple ARP delegates, such as ToR switches, in each location. The broadcast traffic may also be supported by adding a new component to the Port Binding Protocol for the delegates to maintain current updates of all the IP hosts from the servers. Additionally, the L2GW may push down on a periodic or regular basis all the learned host IP addresses from other locations.

In some instances, the L2GW may receive unknown DAs. The L2GW may keep current updates of all the hosts (or applications) in its location and periodically or regularly push its address information to all the peers (other L2GWs in other locations). If the L2GW receives a frame comprising an unknown DA, the L2GW may broadcast the frame to the other locations. To avoid attacks on the network, a limit may be imposed on the maximum number of times the L2GW may forward or broadcast a received unknown DA. The L2GW may be configured to learn the addresses of the intermediate switches in another location to avoid mistaking an intermediate switch address for an unknown address before sending the address to the other location. Although there may be tens of thousands of VMs in each DC location, the number of switches in each DC may be limited, such as the number of ToR or access switches, end of row or aggregation switches, and/or core switches. The L2GW may learn the MAC addresses of all the intermediate switches in a location ahead of time, e.g., via a Bridge Protocol Data Unit (BPDU) from each switch. Messages may not be sent directly to the intermediate switches, except for management system or Operations, Administration, and Maintenance (OAM) messages. An intermediate switch that expects or is configured to receive NMS/OAM messages may allow other switches in the location to learn its MAC address by sending an autonomous message to NMS or a MMRP announcement.

In some embodiments, the L2GWs may use BGP, e.g., instead of IS-IS, for exchanging address information. A plurality of options may be used for controlling Layer 2 (L2) communications. For instance, forwarding options may include Layer 2 only forwarding with MAC and MAC, Layer 2 forwarding over MPLS, and Layer 2 forwarding in Layer 3 network. Options of Layer 2 control plane may include Layer 2 IS-IS mesh control, Layer 2.5 MPLS static control, Label Distribution Protocol (LDP), Resource Reservation Protocol (RSVP)-Traffic Engineering (TE) using Interior Gateway Protocol (IGP) Constraint-based Shortest Path First (CSFP), and BGP discovery. Some VLAN mapping issues may also be considered, such as the VLAN-MAC mapping required for uniqueness and whether Network Bridged VLANs (e.g., VLANs-4K) may be too small for a DC. Table 3 illustrates a plurality of control plane options that may be used for Layer 2 control plane. The options may be based on IEEE 802.1ah, IEEE 802.1q, and IEEE 802.1 aq, all of which are incorporated herein by reference. Table 4 illustrates some of the advantages and disadvantages (pros and cons) of the control plane options in Table 2.

TABLE 3 Layer 2 Control Lane Options MPLS L2 control control Transport plane plane IGP-OSPF/IS-IS BGP L2 Provider 802.1q Not Pass IP-MAC Internal BGP Backbone 802.1ah applicable mapping (IBGP) mesh Bridge External BGP (PBB) (EBGP) mesh VPLS MAC LDP for IGP for CSPF BGP auto- (MPLS) learning domain discovery of interaction RSVP-TE end points with L2 MPLS VPLS ARP static Mediation L2 over IP L2 only Not Peer validation Peer validation with DC applicable Peer connectivity Peer path (802.1aq) Pass IP-MAC connectivity mapping IP-Mapping Explicit distribution multithreading (XMT)

TABLE 4 Control plane options IGP-Open Shortest L2 control MPLS control Path First Transport plane plane (OSPF)/IS-IS BGP L2 PBB No Layer 3 VPLS is done Pros: Pros: configuration IS-IS pass MAC BGP policy address BGP auto-discovery used Multithread (MT)- for the L2 PBB to VPLS VPN mapping ->VLAN BGP efficient for Cons: efficiency for large number of peers and IP mapping I-MAC mappings Multiple VLANs VPLS MAC Pros: Done Pros: Pros: Same as above (MPLS) learning Cons: CSPF for IS- Cons: interaction Code IS/OSPF BGP inter-domain with L2 overhead, Fast peer MPLS interaction with multicast not convergence MPLS Layer 3 (L3) VPN efficient MT topology Cons: not efficient with A) large number of peers B) large number of IP-MAC mappings L2 over IP Limited to Not applicable Peer validation Peer validation only DC Peer connectivity Peer path connectivity IP to MAC mapping IP-Mapping distribution XMT

There may be a plurality of differences between Cisco's OTV and the BGP that may be supported in the virtual Layer 2 network. For instance, OTV basic aspects may include OTV multicast groups, OTV IS-IS usage, which may require MT-IS-IS, and OTV forwarding. Additionally, BGP may support BGP-MAC mapping and IP overlay, such as for DC multicast group. BGP-MAC mapping may also use MT-BGP. Further, IBGP may be supported by MT-IS-IS and using IS-IS for peer topology (e.g., Label Switched Path Verification (LSVP)).

In the virtual Layer 2 network above, the number of applications within one Layer 2 network (or DC) may increase substantially, e.g., over time. Thus, a mechanism may be needed to avoid issues associated with substantially large Layer 2 networks. These issues may include unpredictable behavior of servers/hosts and their applications. For example, the servers/hosts may correspond to different vendors, where some may be configured to send ARP messages and others may be configured to broadcast messages. Further, typical lower cost Layer 2 switches may not have sophisticated features to block broadcast data frames of have policy implemented to limit flooding and broadcast. Hosts or applications may also age out MAC addresses to target IP mapping frequently, e.g., in about minutes. A host may also frequently send out gratuitous ARP messages, such as when the host performs a switch over (from active to standby) or when the host has a software glitch. In some cases, the Layer 2 network components are divided into smaller subgroups to confine broadcast into a smaller number of nodes.

FIG. 15 illustrates an embodiment of a typical broadcast scheme 1500 that may be used in a Layer 2 network/domain, e.g., a VLAN, which may be part of the virtual Layer 2 networks or the pseudo Layer 2 networks above. The Layer 2 network/domain or VLAN may comprise a plurality of access switches (aSs) 1522 located in a Pod 1530, e.g., in a DC. The VLAN may also comprise a plurality of closed user groups (CUGs) 1535 connected to the aSs 1522. Each CUG 1535 may comprise a plurality of End-of-Row (EoR) switches 1524 connected to the aSs 1522, a plurality of ToR switches 1537 connected to the EoR switches 1524, and a plurality of servers/VMs 1539 connected to the ToR switches 1537. The aSs 1522 may be connected to a plurality of Pods (not shown) in other DCs that may correspond to other Layer 2 networks/domains of the virtual Layer 2 networks or the pseudo Layer 2 networks. The components of the Layer 2 network/domain or the Pod 1530 may be arranged as shown in FIG. 15.

The typical broadcast scheme 1500 may suffer from broadcast scalability issues. For instance, frames with unknown DAs may be flooded within the Pod 1530 to all the end systems in the VLAN. For example, the frames with unknown DAs may be flooded to all or plurality of servers/VMs 1539 in the AS 1522 in the CUGs1535, as indicated by the dashed arrows in FIG. 15. The frames with unknown addresses may also be flooded in the opposite direction, via an AS 1522, to a plurality of other Pods (in other DCs) in the core, which may be associated with the same service as the Pod 1530. The frames may be further flooded to a plurality of VMs in the other Pods, which may reach thousands of VMs. Such broadcast scheme for unknown DAs may not be efficient in relatively large networks, e.g., that comprise many DCs.

FIG. 16 illustrates an embodiment of another broadcast scheme 1600 that may be used in a Layer 2 network/domain, e.g., a VLAN, which may be part of the virtual Layer 2 networks or the pseudo Layer 2 networks above. The broadcast scheme 1600 may be more controlled and thus more scalable and efficient than the broadcast scheme 1500. The Layer 2 network/domain or VLAN may comprise a plurality of ASs 1622 located in a Pod 1630, e.g., in a DC. The VLAN may also comprise a plurality of CUGs 1635 connected to the ASs 1622. Each CUG 1635 may comprise a plurality of EoR switches 1624 connected to the ASs 1622, a plurality of ToR switches 1637 connected to the EoR switches 1624, and a plurality of servers/VMs 1639 connected to the ToR switches 1637. The ASs 1622 may be connected to a plurality of Pods (not shown) in other DCs that may correspond to other Layer 2 networks/domains of the virtual Layer 2 networks or the pseudo Layer 2 networks. The components of the Layer 2 network/domain or the Pod 1630 may be arranged as shown in FIG. 16.

To control or limit the broadcast scope of the broadcast scheme 1600, frames with unknown DAs may only be flooded within the Pod 1530 to a single root, for instance to one server/VM 1639 that may be designated as a broadcast server or to an AS 1622. The frames may be flooded to the root using a rooted-multipoint (RMP) VLAN configuration, e.g., a push VLAN tag for RMP VLAN that is rooted at a broadcast server. However, the flooded frame may not be forwarded to all the other servers, e.g., that are not broadcast servers, which may save link resources and server processing of extraneous frames. Additionally, the forwarded frames may not be forwarded to the core, e.g., to other Pods or DCs.

In some embodiments, the broadcast server may hosts a proxy ARP server, a DHCP server, and/or other specific function servers, e.g., for improving efficiency, scalability, and/or security. For instance, the broadcast server may be configured to provide security in DCs that only allow selected broadcast services. If no known service is selected, data frames with unknown DAs may be flooded from the broadcasts server on a first or original VLAN. The broadcast scheme 1600 may be used to handle cases where customer applications are allowed to use Layer 2 broadcast. A data rate limiter may also be used to protect against broadcast storms, e.g., avoid substantial broadcast traffic.

As described above, when introducing server virtualization in DCs, the number of hosts in a DC may increase substantially, e.g., over time. Using server virtualization, each physical server, which may originally host an end-station, may become capable of hosting hundreds of end-stations or VMs. The VMs may be added, deleted, and/or moved flexibly between servers, which may improve performance and utilization of the servers. This capability may be used as a building block for cloud computing services, e.g., to offer client controlled virtual subnets and virtual hosts. The client control virtual subnets offered by cloud computing services may allow clients to define their own subnets with corresponding IP addresses and policies.

The rapid growth of virtual hosts may substantially impact networks and servers. For instance, one resulting issue may be handling frequent ARP requests, such as ARP IP version 4 (IPv4) requests, or neighbor discovery (ND) requests, such as ND IP version 6 (IPv6) requests from hosts. The hosts in a DC may send out such requests frequently due caches or entries that may age in about few minutes. In the case of tens of thousands of hosts in a DC, which may have different MAC addresses, the amount of ARP or ND messages or requests per second may reach more than about 1,000 to 10,000 requests per second. This rate or frequency of requests may impose substantial computational burden on the hosts. Another issue associated with a substantially large number of virtual hosts in a DC may be existing duplicated IP addresses within one VLAN, which may affect the ARP or ND scheme from working properly. Some load balancing techniques may also require multiple hosts which serve the same application to use the same IP address but with different MAC addresses. Some cloud computing services may allow users to use their own subnets with IP addresses and self defined policies among the subnets. As such, it may not be possible to designate a VLAN per each client since the maximum number of available VLANS may be about 4095 in some systems while there may be hundreds of thousands of client subnets. In this scenario, there may be duplicated IP addresses in different client subnets that end up in one VLAN.

In an embodiment, a scalable address resolution mechanism that may be used in substantially large Layer 2 networks, which may comprise a single VLAN that includes a substantial number of hosts, such as VMs and/or end-stations. Additionally, a mechanism is described for proper address resolution in a VLAN with duplicated IP addresses. The mechanism may be used for both ARP IPv4 addresses and ND IPv6 addresses.

FIG. 17 illustrates an embodiment of interconnected network districts 1700 in a bridged Layer 2 network, e.g., an Ethernet. The bridged Layer 2 network may comprise a plurality of core bridges 1712 in a core district 1710, which may be connected to a plurality of districts 1720. The Layer 2 bridged network may also comprise a plurality of DBBs 1722 that may be part of the core district 1710 and the districts 1720, and thus may interconnect the core district 1710 and the districts 1720. Each district 1720 may also comprise a plurality of intermediate switches 1724 connected to corresponding DBBs 1722, and a plurality of end-stations 1726, e.g., servers/VMs, connected to corresponding intermediate switches 1724. The components of the interconnected network districts 1700 may be arranged as shown in FIG. 17.

FIG. 18 illustrates another embodiment of interconnected network districts 1800 that may be configured similar to the interconnected network districts 1700. The interconnected network districts 1800 may comprise a plurality of core bridges 1812 and a plurality of DBBs 1822 (e.g., ToR switches) or district boundary switches in a core district 1810. The interconnected network districts 1800 may also comprise a plurality of intermediate switches 1824 and a plurality of end-stations 1826, e.g., servers/VMs, in a plurality of districts 1820. The districts 1820 may also comprise the DBBs 1822 that connected the districts 1820 to the core district 1810. The components of the interconnected network districts 1800 may be arranged as shown in FIG. 18. A VLAN may be established in the interconnected network districts 1800, as indicated by the bold solid lines in FIG. 18. The VLAN may be associated with a VID and may be established between one of the core bridges 1812 in the core bridge 1810, a subset of the DBBs 1822 in the districts 1820, and a subset of intermediate switches 1824 and servers/VMs 1826 in the districts 1820.

The DBBs 1822 in districts 1820 may be aware and maintain a <MAC,VID> pair for each end-station 1826 in the districts 1820. This address information may be communicated by the end-stations 1826 to the corresponding DBBs 1822 in the corresponding districts 1820 via Edge Virtual Bridging (EVB) Virtual Station Interface (VSI) Discovery and Configuration Protocol (VDP). The DBB 1822 may also register this information with the other DBBs 1822, e.g., via MMRP. Alternatively, the address information may be communicated by the end-stations 1826 to their DBBs 1822 using gratuitous ARP messages or by sending configuration messages from a NMS.

In an embodiment, a scalable address resolution mechanism may be implemented to support a VLAN that comprise a relatively large number of hosts in the interconnected network districts 1800. Specifically, the MAC address of a DBB 1822 in one district 1820 and the VID of the VLAN may be used as a response to an ARP request for the district's host addresses from other districts 1820. In some cases, a DS may be configured to obtain summarized address information for the end-stations 1826 in a district 1820 when the DS may not be capable of handling a relatively large number of messages for individual end-stations 1826 or hosts. In such cases, the DBB 1822 in a district 1820 may terminate all gratuitous ARP messages for the districts hosts or snoop all the gratuitous ARP messages sent from its district 1920, and send out instead a gratuitous group announcement, e.g., that summarizes the hosts address information for the DS. The DBB may send its own gratuitous ARP announcement to announce all the host IP addresses in its district 1820 to other districts 1820.

Further, the DBB 1822 in a district 1820 may serve as an ARP proxy by sending its own MAC address to other districts 1820, e.g., via a core bridge 1812 in the core district 1810. The core bridges 1812 may only be aware of the MAC addresses of the DBBs 1822 in the districts 1820 but not the MAC addresses of the intermediate switches 1824 and end-stations 1826 or hosts, which makes this scheme more scalable. For instance, when a first end-station 1826 in a first district 1820 sends an ARP request for the address of a second end-station 1826 in a second district 1820, the MAC address of a DBB 1822 of the second district 1820 may be returned in response to the first end-station 1826.

FIG. 19 illustrates an embodiment of ARP proxy scheme 1900 that may be used in a Layer 2 bridged network, e.g., for the interconnected network districts 1800. The Layer 2 bridged network may comprise a core district 1910, a plurality of DBBs 1922 or district boundary switches connected to the core district 1910, and a plurality of end-stations 1926 (e.g., VMs) connected to corresponding DBBs 1922 in their districts. The Layer 2 bridged network may also comprise a DS 1940 that may be connected to the DBBs 1922, e.g., via the core district 1910. The DBBs 1922 and end-stations 1926 may belong to a VLAN established in the Layer 2 bridged network and associated with a VID. The components of the Layer 2 bridged network may be arranged as shown in FIG. 19.

Based on the ARP proxy scheme 1900, a first DBB 1922 (DBB X) may intercept an ARP request from a first end-station 1926 in its local district. The ARP request may be for a MAC address for a second end-station 1926 in another district. The ARP request may comprise the IP DA (10.1.0.2) of the second end-station 1926, and the IP source address (SA) (10.1.0.1) and MAC SA (A) of the first end-station 1926. The first end-station 1926 may maintain the IP addresses of the other end-stations 1922 in a VM ARP table 1960. DBB X may send a DS query to obtain a MAC address for the second end-station 1926 from the DS 1940. The DS query may comprise the IP address (10.1.0.2) of the second end-station 1926, and the IP SA (10.1.0.1) and MAC SA (A) of the first end-station 1926. The DS 1940 may maintain the IP addresses, MAC addresses, and information about the associated DBBs 1922 or locations of the end-stations 1926 (hosts) in a DS address table 1950.

The DS 1940 may then return to DBB X a DS response that comprises the IP address (10.1.0.2) of the second end-station 1926 and the MAC address (Y) of a second DBB 1926 (DBB Y) associated with the second end-station 1926 in the other district, as indicated in the DS address table 1950. In turn, DBB X may send an ARP response to the first end-station 1926 that comprises the IP DA (10.1.0.1) and MAC DA (A) of the first end-station 1926, the IP SA (10.1.0.2) of the second end-station 1926, and the MAC address of DBB Y (Y). The first end-station 1926 may then associate the MAC address of DBB Y (Y) with the IP address (10.1.0.2) of the second end-station 1926 in the VM ARP table 1960. The first end-station 1926 may use the MAC address of DBB Y as the DA to forward frames that are intended for the second end-station 1926.

In the ARP proxy scheme 1900, the DBBs 1922 may only need to maintain the MAC addresses of the other DBBs 1922 in the districts without the MAC and IP addresses of the hosts in the districts. Since the DAs in the data frames sent to the DBBs 1922 only correspond to DBBs MAC addresses, as described above, the DBBs 1922 may not need to be aware of the other addresses, which makes this scheme more scalable.

FIG. 20 illustrates an embodiment of a data frame forwarding scheme 2000 that may be used in a Layer 2 bridged network, e.g., for the interconnected network districts 1800. The Layer 2 bridged network may comprise a core district 2010, a plurality of DBBs 2022 or district boundary switches in a plurality of districts 2020 connected to the core district 2010, and a plurality of intermediate switches 2024 and end-stations 2026 (e.g., VMs) connected to corresponding DBBs 2022 in their districts 2020. Some of the DBBs 2022, intermediate switches 2024, and end-stations 2026 across the districts 2020 may belong to a VLAN established in the Layer 2 bridged network and associated with a VID. The components of the Layer 2 bridged network may be arranged as shown in FIG. 20.

The data frame forwarding scheme 2000 may be based on MAT at the DBBs 2022, which may be similar to IP NAT. The MAT may comprise using inner IP DAs and ARP tables to find corresponding MAC DAs. For instance, a first DBB 2022 (DBB1) may receive a frame 2040, e.g., an Ethernet frame, from a first end-station 2026 (host A) in a first district (district 1). The frame 2040 may be intended for a second end-station 2026 (host B) in a second district (district 2). The frame 2040 may comprise a MAC-DA 2042 for a second DBB in district 2 (DBB2), a MAC-SA 2044 for host A (A's MAC), an IP-DA 2046 for host B (B), an IP-SA 2048 for host A (A), and payload. DBB1 may forward the frame 2040 to district 2 via the core district 2010. A second DBB 2022 (DBB2) in district 2 may receive the frame 2040 and replace the MAC-DA 2042 for DBB2 (DBB2) in the frame 2040 with a MAC-DA 2082 for host B (B's MAC) in a second frame 2080. DBB2 may determine B's MAC based on the IP-DA 2046 for host B (B) and a corresponding entry in its ARP table. The second frame may also comprise a MAC-SA 2084 for host A (A's MAC), an IP-DA 2086 for host B (B), an IP-SA 2088 for host A (A), and payload. DBB2 may send the second frame 2080 to host B in district 2. Since the SAs in the received frames at district 2 are not changed, the data frame forwarding scheme 2000 may not affect implemented DHCP in the network.

In the network above, the core bridges or switches of the core district, e.g., the core bridges 1812 in the core district 1810, may only need to maintain the MAC addresses of the DBBs in the districts without the MAC and IP addresses of the hosts in the districts. Since the DAs in the data frames forwarded through the core district may only correspond to DBBs MAC addresses, as described above, the core bridges may not need to be aware of the other addresses. The MAC addresses of the DBBs may be maintained in the core bridges' forwarding databases (FDBs). The core bridges or switches may learn the topology of all the DBBs via a link state based protocol. For example, the DBBs may send out link state advertisements (LSAs), e.g., using IEEE 802.1aq, Transparent Interconnect of Lots of Links (TRILL), or IP based core. If Spanning Tree Protocol (STP) is used among the core bridges, MAC address learning may be disabled at the core bridges. In this case, the DBBs may register themselves with the core bridges.

In an embodiment, the DBBs may act as ARP proxies, as described above, if a DS is not used. Gratuitous ARP messages may be sent by the end-stations to announce their own MAC addresses. Gratuitous group announcements may also be sent by the DBBs to announce their own MAC addresses and the IP addresses for all the hosts within their local districts. The gratuitous group announcements may be used to announce the MAC and IP addresses to the other DBBs in the other districts. The announced MAC addresses and IP addresses may be used in the other DBBS to translate DBB MAC DAs in received frames according to host IP DAs. A gratuitous group ARP may be sent by a DBB to announce a subset of host IP addresses for each VLAN associated with the DBB. The gratuitous group ARP may comprise a mapping of subsets of host IP addresses to a plurality of VLANs for the DBB.

Table 5 illustrates an example of mapping host IP addresses to the corresponding DBB MAC addresses in the interconnected districts. The mapping may be sent in a gratuitous group ARP by a DBB to announce its host IP addresses for each VLAN associated with the DBB. A DBB MAC address (DBB-MAC) may be mapped to a plurality of corresponding host IP addresses. Each DBB MAC address may be mapped to a plurality of host IP addresses in a plurality of VLANs (e.g., VID-1, VID-2, VID-n, . . . ), which may be in the same or different districts.

TABLE 5 Information carried by Gratuitous Group ARP DBB VLAN Host DBB-MAC VID-1 IP addresses of all hosts in this VLAN (IP Prefix) VID-2 IP addresses of all hosts in this VLAN (IP Prefix) VID-n IP addresses of all hosts in this VLAN (IP Prefix)

In some situations, multiple hosts in the interconnected districts may have the same IP addresses and may be associated with the same VLAN (or VID). For instance, a virtual subnet of a cloud computing service may allow clients to name their own private IP addresses. The number of virtual subnets offered by a cloud computing service may substantially exceed the total number of allowed VLANs (e.g., about 4095 VLANs). As such, a plurality of virtual hosts (e.g., VM or virtual end-stations) may be allowed to have the same IP addresses but with different MAC addresses. In other instances, multiple end-stations may serve the same application using the same IP addresses but different MAC addresses.

In an embodiment, a DBB may be assigned a plurality of MAC addresses, referred to herein as delegate MAC addresses, e.g., to differentiate between different hosts that use the same (duplicated) IP address. The DBB may also be associated with a plurality of VLANs. Further, each VLAN on the DBB may be associated with a plurality of subnets or virtual subnets, e.g., that comprise different subsets of hosts within the VLAN. The virtual subnets may be associated with a plurality of subnet identifiers (IDs). If the number of duplicated IP addresses for the hosts is substantially less than the number of virtual subnets of the VLAN, then the number of delegate MAC addresses for the DBB may also be substantially less.

FIG. 21 illustrates an embodiment of an ARP proxy scheme 2100 that may be used for interconnected network districts in a Layer 2 bridged network. The Layer 2 bridged network may comprise a core district 2110, a plurality of DBBs 2122 or district boundary switches connected to the core district 2110, and a plurality of end-stations 2126 (e.g., VMs) connected to corresponding DBBs 2122 in their districts. The Layer 2 bridged network may also comprise a DS 2140 that may be connected to the DBBs 2122, e.g., via the core district 2110. The DBBs 2122 and end-stations 2126 may belong to a VLAN established in the Layer 2 bridged network. The components of the Layer 2 bridged network may be arranged as shown in FIG. 21.

Based on the ARP proxy scheme 2100, a first DBB 2122 (DBB X) may intercept an ARP request from a first end-station 2226 in its local district. The ARP request may be for a MAC address for a second end-station 2126 in another district. The ARP request may comprise the IP DA (10.1.0.2) of the second end-station 2126, and the IP SA (10.1.0.1) and MAC SA (A) of the first end-station 2126. The first end-station 2126 may maintain the IP addresses of the other end-stations 2122 in a VM ARP table 2160. DBB X may then forward a DS query to obtain a MAC address for the second end-station 2126 from the DS 2140. The DS query may comprise the IP address (10.1.0.2) of the second end-station 2126, and the IP SA (10.1.0.1) and MAC SA (A) of the first end-station 2126. The DS 2140 may maintain the IP addresses, MAC addresses, VLAN IDs or VIDs, customer (virtual subnet) IDs, and information about the associated DBBs 2122 or locations of the end-stations 2126 in a DS address table 2150.

The DS 2140 may use the MAC SA (A) in the DS query to determine which customer (virtual subnet) ID belongs to the requesting VM (first end-station 2126). For example, according to the DS address table 2150, the customer ID, Joe, corresponds to the MAC SA (A). The DS 2140 may then return to DBB X a DS response that comprises the IP address (10.1.0.2) of the second end-station 2126 and a delegate MAC address (Y1) of a second DBB 2126 (DBB Y) associated with the customer ID (Joe) of the first end-station 2126. In turn, DBB X may send an ARP response to the first end-station 2126 that comprises the IP DA (10.1.0.1) and MAC DA (A) of the first end-station 2126, the IP SA (10.1.0.2) of the second end-station 2126, and the delegate MAC address of DBB Y (Y1). The first end-station 2126 may then associate the delegate MAC address of DBB Y (Y1) with the IP address (10.1.0.2) of the second end-station 2126 in the VM ARP table 2160. The first end-station 2126 may use the delegate MAC address of DBB Y as the DA to forward frames that are intended for the second end-station 2126.

A third end-station 2126 in another district may also send an ARP request for the second end-station 2126 to a corresponding local DBB 2122 (DBB Z) in the third end-station's district. DBB Z may then communicate with the DS 2140, as described above, and return accordingly to the third end-station 2126 an ARP response that comprises the IP DA (10.1.0.3) and MAC DA of the third end-station 2126, the IP SA (10.1.0.2) of the second end-station 2126, and a delegate MAC address of DBB Y (Y2) associated with the customer ID, Bob, of the third end-station 2126 in the DS address table 2150. The third end-station 2126 may then associate the delegate MAC address of DBB Y (Y2) with the IP address (10.1.0.2) of the second end-station 2126 in a VM ARP table 2170 of the third end-station 2126. The third end-station 2126 may use this delegate MAC address of DBB Y as the DA to forward frames that are intended for the second end-station 2126.

Table 6 illustrates an example of mapping a duplicated host IP address to corresponding delegate DBB MAC addresses in a VLAN in the interconnected districts. The duplicated host address may be used by a plurality of hosts for one intended application or host. The delegate MAC DBB addresses may be assigned for the different hosts that use the same application (or communicate with the same host). For each VLAN, a host IP address may be mapped to a plurality of delegate DBB MAC addresses (MAC-12, MAC-13, MAC-14, . . . ) for a plurality of hosts, e.g., associated with different subnets of the VLAN. The delegate DBB MAC addresses may also be associated with a base (original) DBB MAC address (MAC-11). The base and delegate DBB MAC addresses for the same IP may be different for different VLANs. When a VLAN does not have delegate addresses, the DBB base address may be used for the VLAN. If there are about 10 duplicated IP addresses within one VLAN, then about 10 columns (ten MAC addresses) in the table 6 may be used.

TABLE 6 MAT for Duplicated IP addresses. DBB Base DBB DBB DBB DBB IP Address Address Delegate 1 Delegate 2 Delegate 3 Delegate 4 . . . 10.1.0.1 MAC-11 MAC-12 MAC-13 MAC-14 (VLAN#1) 10.1.0.1 MAC-21 MAC-22 . . . (VLAN#2) 10.1.0.1 MAC-31 . . . (VLAN#3)

Table 7 illustrates an example of mapping host IP addresses to a plurality of delegate MAC addresses, e.g., for multiple subnets. The mapping may be sent in a gratuitous group ARP by a DBB to announce its host IP addresses for each VLAN associated with the DBB. Each delegate MAC address (DBB-MAC1, DBB-MAC2, . . . ) may be mapped to a plurality of corresponding host IP addresses in a subnet. Each delegate DBB MAC address may be associated with a customer or virtual subnet ID for the host IP addresses. The host IP addresses for each delegate DBB MAC address may also correspond to a plurality of VLANs (VID-1, VID-2, VID-n, . . . ). The host IP addresses in each subnet may be different. Duplicated host IP addresses, which may be associated with the same VLANs but with different customer IDs, may be mapped to different delegate DBB MAC addresses.

TABLE 7 Information carried by Gratuitous Group ARP DBB VLAN Host DBB-MAC1 VID-1 IP addresses of all hosts in this VLAN (IP Prefix) VID-2 IP addresses of all hosts in this VLAN (IP Prefix) VID-n IP addresses of all hosts in this VLAN (IP Prefix) DBB-MAC2 VID-1 IP addresses of all hosts in this VLAN (IP Prefix) VID-2 IP addresses of all hosts in this VLAN (IP Prefix) VID-n IP addresses of all hosts in this VLAN (IP Prefix)

FIG. 22 illustrates an embodiment of a fail-over scheme 2200 that may be used for interconnected network districts in a Layer 2 bridged network. The fail-over scheme 2100 may be used in the case any of the DBBs (e.g., a ToR switch) in the interconnected districts fails. The Layer 2 bridged network may comprise a plurality of core bridges 2212 and a plurality of DBBs 2222 or district boundary switches in a core district 1810, and a plurality of districts 2220. The districts 2220 may comprise the DBBs 2222, a plurality of intermediate switches 2224, and a plurality of end-stations 2226, e.g., servers/VMs. The Layer 2 bridged network may also comprise a DS (not shown) that may be connected to the DBBs 2222, e.g., via the core district 2210. Some of the DBBs 2222, intermediate switches 2224, and end-stations 2226 may belong to a VLAN established in the Layer 2 bridged network. The components of the Layer 2 bridged network may be arranged as shown in FIG. 22.

When an active DBB 2222 fails in a VLAN, the VLAN may be established using one or more standby DBBs 2222. The standby DBBs 2222 may establish active connections with at least some of the intermediate switches 2224 that belong to the VLAN and possibly with a new core bridge 2212. This is indicated by the dashed lines in FIG. 22. As such, the paths to the end-stations 2226 of the VLAN may not be lost which allows the end-stations 2226 to communicate over the VLAN. When the DBB 2222 in the VLAN fails, the DS may be notified of the failure, for instance by sending an explicit message to the DS or using a keep-alive method. Thus, a DBB may replace the address information of the failed DBB and possibly other original DBBs 2222 in the VLAN in the entries of the DS address table with information of the new DBBs 2222 that were on standby and then used to replace the failed and other original DBBs 2222. A replaced failed and original DBB are indicated by circles in FIG. 30. Upon detecting the failed DBB 2222, a replacement DBB may send a LSA to the DS or the core district 2010 to indicate that the failed DBB's addresses, including all delegate addresses, are reachable by the replacement DBB 2222.

Ethernet-based large L2 networks may be used in DCs to improve network agility in order to better support server virtualization and dynamic allocation of resources across relatively large server pools. For such large L2 networks with potentially a large number of virtual hosts, the traditional Ethernet with STP may not be any longer suitable due to the following limitations: (1) low link bandwidth utilization due to the spanning tree, (2) MAC forwarding table scalability issue due to the flat MAC address space, and (3) broadcast storm caused by ARP and/or other broadcast traffic, such as DHCP. Several solutions were proposed to build large L2 networks, including: [1] Virtual Layer 2 (VL2) by A. Greenberg et al. in “Towards a Next Generation Data Center Architecture: Scalability and Commoditization”, published in PRESTO 08, [2] Transparent Interconnection of Lots of Links (TRILL) by R. Perlman et al. in “Rbridges: Base Protocol Specification”, published in IETF draft-ietf-trill-rbridge-protocol-12.txt, [3] Short Path Bridging (SPB) published in IEEE P802.1aq/D2.5, Jan. 6, 2010, [4] PortLand by R. Myscore et al. in “PortLand: A Scalable Fault-Tolerant Layer 2 Data Center Network Fabric”, published in SIGCOMM'09, and [5] Multi-level Origin-Organized Scalable Ethernet (MOOSE) by M. Scott et al. in “Addressing the Scalability of Ethernet with MOOSE”, published in ITC'21 DC-CAVES Workshop, 2009, all of which are incorporated herein by reference.

The solutions above may have the following in common: (1) using the shortest path forwarding to replace the STP and (2) making the core switches in the network agnostic to the host MAC addresses. The shortest paths between any two switches in the network may be calculated either in a distributed fashion (e.g., based on the network topology obtained via routing protocols), such as in references [1] and [2] above, or in a centralized manner, such as in reference [4]. In a large L2 network, a host IP address may lose its location information and the edge switch that the host connects to may become its location. Thus, the host local information may be specified by the edge switch ID, which may be usually in the form of IP address or MAC address. The edge switch may also be referred to as a Top-Of-Rack (TOR) switch or access switch in DCs. The existing large L2 solutions may differ in how the host location information is used in forwarding frames from ingress edge switches to egress edge switches.

The encapsulation of host location information on top of the original Ethernet frames is used in references [1], [2], and [3] above. The encapsulation may be performed by the local hosts, as in reference [1], or by the edge switches, as in references [2] and [3]. The VL2 of reference [1] may be substantially scalable but requires change to the host Operation System (OS). The TRILL [2] and SPB [3] solutions may require no change to the host OS but may have potential MAC forwarding table scalability issues as each edge switch may need to keep track of at least the local MAC addresses and the remote MAC addresses that are involved in communicating with the local MAC addresses, even if a selective MAC learning is enabled. For the PortLand [4] and MOOSE [5] solutions, an edge switch may map a local host MAC address to a pseudo MAC address, which may have the host location information encoded. In these two solutions, the host ARP cache table may store pseudo MAC addresses instead of the real MAC addresses and the pseudo MAC addresses may be used to forward frames across the network similar to the TRILL [2] and SPB [3] solutions. The PortLand [4] and MOOSE [5] solutions may not require any change to the host OS. Unlike TRILL and SPB, the PortLand and MOOSE may be substantially scalable as the forwarding table size in edge switches may be proportional to the number of local MAC addresses and the number of switches in the network. Furthermore, logically centralized DS may be required in references [1], [4], and [5]. But in general, the DS may also be used in other solutions to significantly reduce or eliminate ARP and DHCP broadcast traffic.

A new large L2 solution is described below in which a MAC address delegation scheme is used. Accordingly, each switch may be assigned one or more MAC addresses, which may be used as the delegates for the MAC addresses of hosts connected to the switch. The delegate MAC addresses may specify the location of hosts and may be used by the network to forward frames from ingress switches to egress switches, e.g., edge switches. Compared to the MAC mapping scheme described in PortLand [4] and MOOSE [5], the host ARP cache table in the new scheme stores the delegate MAC addresses instead of the pseudo MAC addresses. The proposed solution described below is substantially scalable and has some advantages over the solutions in [4] and [5], such as: (1) simplifying the MAC address management at the edge switches; (2) simplifying the handling of edge switch failure; (3) and requiring no table lookup for source MAC address rewriting at ingress edge switches if only one switch MAC address is used. Further, the MAC mapping scheme described in references [4] and [5] may correspond to a special case of the MAC delegation scheme proposed herein.

The proposed MAC address delegation scheme may support substantially scalable Ethernet networks with duplicated host IP addresses and duplicated VLAN IDs. Specifically, each switch may be assigned a set of MAC addresses, which may be used as the delegates and location information for the MAC addresses of hosts connected to the switch. The set of MAC addresses per switch may allow resolving the duplicated IP addresses of hosts connected to the same switch. The scheme may also use an ARP proxy and location server to register VMs and disseminate the VM location information. Link and node failure recovery methods are also described below for the MAC address delegation scheme.

In an embodiment, the large L2 network under consideration may comprise a plurality of core switches, edge switches connected to the core switches, and servers (or hosts) connected to the edge switches. The edge switches may correspond to TOR switches or access switches in DCs. With server virtualization, a physical server may comprise one or more virtual severs (e.g., virtual hosts or VMs) within a physical server. A physical sever that comprises multiple VMs that are connected to one or more edge switches may also comprise a plurality of virtual switches, e.g., as described in [6] “Edge Virtual Bridge Proposal”, Version 0, Rev. 0.1, IEEE802.1Qbg Working Group, Apr. 23, 2010, which is incorporated herein by reference. In the case of blade servers, there may be a blade switch positioned between a physical server and the edge switches. In general, there may be one or more switches positioned between a VM and an edge switch. Typically, STP is not enabled on the virtual switches and the blade switches, and each VM may access the network only via one edge switch. Thus, without loss of generality, a VM may be connected logically to one edge switch at any given time for communications with other VMs residing in different physical servers and/or for communications with VMs residing in the same physical server via virtual switches configured in a Virtual Ethernet Port Aggregation (VEPA) mode, as described in reference [6] above.

Each VM may also comprise one virtual Network Interface Card (vNIC) with a MAC address that may be unique within the network scope under consideration. Each VM may be assigned an IP address, which may or may not be unique within the network. To handle the case of VMs with non-unique or duplicated IP addresses, each edge switch in the network may be assigned a set of MAC addresses. For instance, a switch X may be assigned a set of n MAC addresses {x₀, x₁, . . . , x_(n-1)}, where n is an integer. The n switch MAC addresses may be assigned in a compact manner based on an address prefix. For instance, the first about 4 octets of a MAC address may be used as a switch MAC address prefix and the last about 2 octets (referred to as MAC address suffix) may be used to indicate each individual switch MAC address within the set. For example, the MAC address prefix of switch X may be 02-11-11-11. When n=8, x₀=02-11-11-11-00-00, x₁=02-11-11-11-00-01, . . . , and x₇=02-11-11-11-00-07 may be assigned for switch X. In this scenario, x₀ is referred to as the base MAC address of switch X, and x₁ to x_(n-1) are referred to as the extended MAC addresses of switch X.

Additionally, switch Y may be a second switch that forms a protection/redundant pair with switch X and may be assigned a set of m MAC addresses {y₀, y₁, . . . , y_(m-1)} with prefix 02-22-22-22 (m is an integer). The suffix of MAC addresses of switch Y may be distinct from the suffix of MAC addresses of switch X. For example, if {a₀, a₁, . . . , a_(n-1)} and {b₀, b₁, . . . , b_(m-1)}are the sets of address suffix of switch X and Y, respectively, then {a₀, a₁, . . . , a_(n-1)}∩{b₀, b₁, . . . , b_(m-1)}=0. In the above example, when m=16, y₀=02-22-22-22-10-00, y₁=02-22-22-22-10-01, . . . , and y₁₅=02-22-22-22-10-0F. may be assigned for switch Y. In general, the switch MAC address prefix may not have to be fixed as long as the prefix may accommodate enough MAC addresses for the switch itself and its protection switch.

For a given MAC address of switch X, for example x_(k), where k=0, 1, . . . , n−1, every switch in the network may be able to forward Ethernet frames with destination MAC (DMAC) of x_(k) along the shortest paths to switch X. The switch's MAC address information may be disseminated using a link-state routing protocol such as IS-IS. A new IS-IS Type Length Value (TLV) may be defined which specifies the switch MAC address prefix. This new TLV may be advertised with other TLVs via IS-IS Link State Protocol Data Units (LSPs). Alternatively, a centralized path computing engine may be used for the entire network, which may be implemented on a physical server or a set of VMs. The computing engine may have the network topology information and the MAC addresses of all the switches. The computing engine may calculate the shortest paths between switch pairs and may download the resulting MAC forwarding tables to individual switches. In either of the approaches above, frame forwarding in the network may be based on the DMAC of the frames. Additionally, the flooding of frames with unknown DMAC may be disabled in the network. The data path MAC learning may also be disabled in the network. As such, frames with unknown DMAC may be simply discarded.

In some scenarios, each switch may have only one MAC address (i.e. no duplicated IP addresses are allowed). Accordingly, the MAC address delegation scheme may comprise using the MAC address of an edge switch as the delegate and the location information for the MAC addresses of the VMs connected to the edge switch. Specifically, each entry of an ARP cache table of a VM may store the switch (edge switch) MAC address of a remote VM (connected to the edge switch) rather than the actual MAC address of the remote VM. Thus, when the VM sends an Ethernet frame to a remote VM, the DMAC of the frame may comprise the MAC address of the edge switch that the remote VM connects to. This DMAC may then be used by the network to forward the frame. Thus, the forwarding table size of edge switches may be proportional to the number of the local MAC addresses and the number of switches in the network, which reduces the amount of stored/exchanged information and makes the scheme substantially scalable. The MAC address delegation scheme may use an ARP proxy at the edge switches and a location server (LS). More details on the ARP processing and the LS are describe below for the duplicated IP address case. A data frame forwarding scheme using the MAC address delegation scheme is also described below.

In an embodiment, the LS may provide a DS, which may be implemented on a logically centralized server (e.g., either a set of physical servers or a set of VMs). For each VM, the information stored in the LS may comprise the following: a customer ID, an IP address, a MAC address, a VLAN ID, a switch MAC address (i.e. VM location information), and optionally other information. The customer ID may be useful in the duplicated IP address scenario where the same IP address may be used by multiple VMs from different customers. The customer ID may be an n-octet unsigned number. A customer ID may be associated with a MAC address before it is assigned to a VM.

FIG. 23 illustrates an embodiment of a VM registration scheme 2300 that may be used in the MAC address delegation scheme. In the VM registration scheme 2300, each edge switch 2360 in the network may act as an ARP proxy for the VMs connected to the edge switch 2360. When an edge switch 2360 receives an ARP request frame from a VM, the frame may be forwarded to an ARP proxy module 2366 in the edge switch 2360. The ARP proxy module 2366 may check if a <source MAC (SMAC), source IP> address pair in the frame is found in an ARP table 2368 of the edge switch 2360. If a match for the address pair is found in the ARP table 2368, then the ARP proxy module 2366 may perform regular ARP processing of the frame. Otherwise, the ARP proxy module 2366 may register the VM and then perform the regular ARP processing. The VM registration process may be implemented as follows. A VM registration (VMR) or location registration (LR) module 2364 may assign a switch MAC address to the VM and then send a registration message to a LS 2340 connected to the edge switch 2360 in the network. The LR module 2364 may assign the switch MAC address from a switch MAC address DB 2362 of the edge switch 2362. The registration message may comprise the following information: an IP address, a MAC address, a VLAN ID, and a switch MAC address.

Upon receiving the registration message, the LS 2340 may use the MAC address in the message to find a corresponding customer ID in a customer MAC database (DB) 2342 coupled to the LS 2340. The LS 2340 may then update a LS database (LSDB) 2344 coupled to the LS 2340, and may send back a confirmation message to the edge switch 2360. The customer MAC DB 2342 may be managed by another entity than the LS 2340 that may be located elsewhere in the network.

After receiving a registration confirmation message from the LS 2340, the VMR or LR module 2364 may request from the ARP proxy module 2366 to update the ARP table 2368. The LR module 2364 may also inform a FDB Manager 2370 of the edge switch 2360 to add a new entry in a corresponding FDB 2372 and update the FDB 2372 on the data path. The ARP table 2368 content may comprise a subset of the LSDB 2344 content. The information stored in each FDB 2372 entry in the edge switch 2360 is described further below. A network facing FDB may also be populated using a link-state routing protocol, where each entry may comprise a switch MAC address prefix and one or more outgoing port ID(s) to reach that prefix.

The procedure of assigning a switch MAC address to a VM may be implemented as follows. The VMR or LR module 2362 may attempt to assign the switch base MAC address (e.g., x₀ in case of switch X in the example above) to the VM. If another VM with the same IP address has already been assigned to the base MAC address, the VMR or LR module 2362 may attempt the next switch MAC address (e.g., the extended switch MAC address x₁) and so on, until a switch MAC address is found. If the VMs connected to the edge switch 2360 have no duplicated IP addresses, then only the switch base MAC address may be used. Otherwise, more than one switch MAC address may be used as described below.

In an embodiment, the edge switch 2360 may also act as a DHCP proxy for the VMs connected to the edge switch 2360. The VM registration may be triggered after the DHCP process is successfully completed. The VM registration may also be triggered after receiving a frame with unknown SMAC. The LS 2340 may also deny a VM registration, e.g., failing the security check. In this case, the edge switch 2360 may choose to discard frames received from that <MAC address, IP address> pair.

Table 8 illustrates an example of the LSDB 2344. As shown, each LSDB 2344 entry may comprise a customer ID, an IP address, a MAC address, a VLAN ID, and a switch MAC address (e.g., location information). If multiple LSDB 2344 entries comprise duplicated (same) IP addresses, then the LSDB 2344 entries may comprise different customer IDs.

TABLE 8 LSDB Customer IP VLAN Switch MAC ID Address MAC Address ID Address (Location) 10 10.1.0.1 00-0C-29-00-00-01 100 02-11-11-11-00-00 20 10.1.2.1 00-0C-29-00-00-50 200 02-11-11-11-00-00 30 10.1.0.1 00-0C-29-00-A0-B2 300 02-11-11-11-00-01 10 10.1.0.2 00-0C-29-00-10-DE 100 02-33-33-33-00-00 20 10.1.2.5 00-0C-29-00-00-60 200 02-22-22-22-00-00 10 10.1.0.7 00-0C-29-00-00-A0 100 02-44-44-44-00-00

Table 9 illustrates an example of the ARP table 2368. As shown, each ARP table 2368 entry may comprise a host IP address, a host MAC address, a customer ID, a VLAN ID, and a switch MAC address (e.g., location information). If multiple ARP table 2368 entries comprise duplicated (same) IP addresses, then the ARP table 2368 entries may comprise different customer IDs.

TABLE 9 ARP Table Switch MAC Host IP Customer VLAN Address Address Host MAC Address ID ID (Location) 10.1.0.1 00-0C-29-00-00-01 10 100 02-11-11-11-00-00 10.1.0.1 00-0C-29-00-A0-B2 30 300 02-11-11-11-00-01 10.1.2.1 00-0C-29-00-00-50 20 200 02-11-11-11-00-00 10.1.0.2 00-0C-29-00-10-DE 10 100 02-33-33-33-00-00 10.1.0.7 00-0C-29-00-00-A0 10 100 02-44-44-44-00-00

Table 10 illustrates an example of the FDB 2372 for local hosts (e.g., VMs) connected to an edge switch with a switch MAC address prefix 02-11-11-11. As shown, each FDB 2372 entry may comprise a switch MAC address suffix (e.g., location information), an IP address, a MAC address, a VLAN ID, and an output port. If multiple FDB 2372 entries comprise duplicated (same) IP addresses, then the FDB 2372 entries may comprise different switch MAC suffix. Table 11 illustrates an example of the FDB 2372 for remote hosts (or VMs) connected to other edge switches.

TABLE 10 FDB for Local Hosts Switch MAC Address IP Suffix (Location) Address MAC Address VLAN ID Output Port 00-00 10.1.0.1 00-0C-29-00-00- 100 1 01 00-00 10.1.2.1 00-0C-29-00-00- 200 2 50 00-01 10.1.0.1 00-0C-29-00-A0- 300 3 B2

TABLE 11 FDB for Remote Hosts Switch MAC Address Prefix (Location) VLAN ID Output Port 02-33-33-33-00-00/32 100 5 02-44-44-44-00-00/32 100 10

FIG. 24 illustrates an embodiment of a LS registration message payload 2400 and a LS confirmation message payload 2420, which may be used in the VM registration scheme 2300. The LS registration message payload 2400 and the LS confirmation message payload 2420 may be sent in User Datagram Protocol (UDP) packets with specific UDP port numbers. The LS registration message payload 2400 may comprise a Type 2402, a Length 2404, a sequence number 2406, a host IP address 2408, a host MAC address 2410, a VLAN ID 2412, and a switch MAC address 2414. The LS confirmation message payload 2420 may comprise a Type 2422, a Length 2424, a sequence number 2426, a host IP address 2428, a host MAC address 2430, a VLAN ID 2432, a switch MAC address 2434, and a customer ID 2436.

The Type 2402 may be set to about zero to indicate a LS registration message. The sequence number 2406 and sequence number 2426 may be used to match the LS confirmation message with the LS registration message. The LS confirmation message payload 2420 may comprise the same registration information in the LS registration message payload 2400 in addition to the customer ID 2436. However, unlike the Type 2402, the Type 2422 may be set to about one to indicate a LS confirmation message. Additionally, the LS registration message may comprise a source IP address that corresponds to the switch (edge switch) IP address and a destination IP address that corresponds to the LS IP address.

FIG. 25 illustrates an embodiment of an ARP processing scheme 2500 that may be used in the MAC address delegation scheme. In the ARP processing scheme 2500, upon receiving an ARP request from a first VM (VM1) 2526, an ARP proxy (ARP proxy module) in an edge switch (edge switch X) 2522 may use the sender's IP address and MAC address (in the ARP request) to find the customer ID in the ARP table (of the edge switch 2522). The ARP proxy may then use the target IP address (in the ARP request) and the customer ID to find the target MAC address in another table which may comprise the same information as the ARP table. If the target MAC address is found, then the ARP proxy may send back to VM1 an ARP reply. If the target MAC address is not in the ARP table, then the ARP proxy may send a LS or DS query message to a LS 2540, which may comprise a DS.

Upon receiving the LS or DS query message, the LS 2540 may use the target IP address and customer ID in the payload of the DS query message to obtain the target MAC address in a LSDB of the LS 2540. If the target MAC address is found, then the LS 2540 may send back to the edge switch 2522 a LS or DS response message. If no target MAC address is found, then the LS 2540 may send a broadcast message to all the (edge) switches in the network to find the target MAC address. The broadcast message may be in the regular ARP request format or in other type of packet format. Each edge switch 2522 that receives the broadcast message may send out a regular ARP request on its server facing ports. The edge switches 2522 that receive the ARP reply may register the corresponding VMs to the LS 2540. Upon receiving a LS or DS response message, the ARP proxy module of edge switch X may send an ARP reply to the sender of the ARP request, e.g., VM1.

In the ARP reply, the target MAC address may not be the real MAC address (e.g., B) of the target VM but the location (e.g., z_(o)) of the target VM, which may correspond to one of the MAC addresses of the (edge) switch that the target VM is connected to. Consequently, the host ARP table of edge switch X may store the switch MAC address instead of the target MAC address. Further, to reduce unnecessary queries to the LS 2540, each edge switch 2522 may cache target VM information in its ARP table. An edge switch 2522 may be responsible for refreshing its ARP table entries for the local VMs by periodically sending out ARP requests. The ARP table entries for remote VMs may expire after a predefined time interval. In the ARP processing scheme 2500, the sender and target VMs may not be in the same VLAN. If the sender and target VMs are required to be in the same VLAN, then the VLAN ID may be checked during the ARP processing. If the two VMs are in different VLANs, then no ARP reply may be sent to the sender of the ARP request.

In an embodiment, after sending an ARP reply to VM1, edge switch X may also send an ARP reply to another VM 2526 (VM2) to allow VM2 to learn the MAC address of VM1. Specifically, edge switch X may send a unicast ARP reply to a second edge switch 2522 (edge switch Z) connected to VM2 with DMAC=z0. The ARP reply may be forwarded from edge switch X to edge switch Z via a network core 2510. Edge switch Z may then forward the ARP reply to VM2 using a Target Hardware Address (THA) and a Target Protocol Address (TPA) in the ARP reply payload.

FIG. 26 illustrates an embodiment of a LS query message payload 2600 and a LS response message payload 2620, which may be used in the ARP processing scheme 2500. Similar to the LS registration and confirmation messages in the VM registration scheme 2300, the LS query and response messages in the ARP processing scheme 2500, may be sent as UDP packets. The LS query message payload 2600 may comprise a Type 2602, a Length 2604, a sequence number 2606, an ARP payload 2608, and a sender customer ID 2610. The LS response message payload 2620 may comprise a Type 2622, a Length 2624, a sequence number 2626, an ARP payload 2628, a real sender hardware address (SHA) 2630, a VLAN ID 2632, and a target customer ID 2634.

The Type 2602 may be set to about two to indicate a LS query message. The sequence number 2606 and sequence number 2426 may be used to match the LS query message with the LS response message. The Type 2622 may be set to about three to indicate a LS reply message. The ARP payloads 2608 and 2628 may comprise the same information as a regular or standard ARP payload. For instance, in the ARP processing scheme 2500, the ARP payload 2608 may comprise a SHA=A, a sender protocol address (SPA)=10.1.0.1, a THA=0, a TPA=10.1.0.2. The ARP payload 2628 may comprise a SHA=z0, a SPA=10.1.0.2, a THA=A, and a TPA=10.1.0.1. The LS response payload 2620 may comprise the real SHA 2630=B and the corresponding target customer ID.

In the VM registration scheme 2300 and the ARP processing scheme 2500, each VM may comprise one vNIC. However, in some networks, one VM may have one IP address but two or more vNICs with distinct MAC addresses. These MAC addresses may usually be in different VLANs and/or may belong to different user groups. The different user groups may belong to the same customer. If the VMs of one user group use only one VLAN, then the above ARP processing schemes may still be valid by additionally checking the VLAN ID. If the VMs of one user group may use different VLANs, then a group ID may be introduced under the customer ID to further identify a VM and the above ARP processing schemes may still be valid.

In the MAC address delegation scheme, a set of MAC addresses may be assigned to an edge switch in the form of, for instance, a MAC address prefix. For a gateway that may be implemented in a core switch, a set of MAC addresses may also be assigned for a different purpose. A gateway MAC address may be assigned to a customer's IP subnet. When a frame destined to the gateway is received, the suffix of the frame DMAC may be used to find the IP forwarding table and the destination IP address of the frame may be used in the table lookup. If a match is found, then the packet may be forwarded. Otherwise, a table lookup may be performed in the default IP forwarding table. If a match is found, then the packet may be forwarded. Otherwise, the packet may be discarded.

FIG. 27 illustrates an embodiment of a data frame forwarding scheme 2700 that may be used in the MAC address delegation scheme. In the data frame forwarding scheme 2700, the ARP table entry at a first VM (VM1) 2726 for the IP address 10.1.0.2 of a second VM (VM2) 2726 may be the MAC address z₀ of an edge switch 2722 (edge switch Z) connected to VM2. When VM1 sends a frame to VM2, VM1 may use the DMAC of z_(o). An ingress edge switch 2722 (edge switch X) connected to VM1 may use the DMAC to forward the frame to the egress edge switch Z via a plurality of core switches 2712 in a network core 2710. The forwarding may also be based on the DMAC at intermediate (edge) switches along the path. When edge switch Z receives the frame, edge switch Z may use the switch MAC address suffix in the DMAC and the destination IP address (in the frame) to perform a lookup in the forwarding table (e.g., similar to FDB 2372) of edge switch Z to obtain the DMAC and a VLAN ID of VM2 and hence forward the frame to VM2. In this scenario, the SMAC of the frame may remain unchanged end to end (on the path from VM1 to VM2). However, the frame VLAN ID may or may not be changed in edge switch Z, e.g., depending on whether VM1 and VM2 are in different VLANs or in the same VLAN.

FIG. 28 illustrates an embodiment of another data frame forwarding scheme 2800 that may be used in the MAC address delegation scheme. In the data frame forwarding scheme 2800, the ARP table entry at a first VM (VM1) 2826 for the IP address 10.1.0.2 of a second VM (VM2) 2826 may be the MAC address z_(o) of an edge switch 2822 (edge switch Z) connected to VM2. When VM1 sends a frame to VM2, VM1 may use the DMAC of z_(o), as in the data frame forwarding scheme 2700. The frame may be sent from VM1 to VM2 via an edge switch 2822 (edge switch X) connected to VM1, a plurality of core switches 2812 in a network core 2810, and edge switch Z. However, in the data frame forwarding scheme 2800, the ingress edge switch X may change the SMAC from MAC A to MAC x₀, which may be useful in some network scenarios that may expect VM2 to see SMAC x₀ instead of true SMAC A. In this case, one additional lookup may be required at ingress edge switch X to use the frame SMAC to get switch MAC address x₀ or more specifically, the suffix of x₀. Edge switch X may then change the frame SMAC to x₀ before sending the frame out. The SMAC may then remain unchanged on its path to VM2. The additional lookup may be omitted if edge switch X uses only one switch MAC address, which may be an advantage over the MAC address mapping methods in references [4] and [5] above in this scenario. In general, if VM2 does not care about the SMAC, the egress edge switch Z may act like a normal gateway by replacing the frame SMAC with the egress edge switch Z's own MAC address.

The data frame forwarding scheme 2700 or the data frame forwarding scheme 2800 may also be used in the case where VM1 and VM2 are connected to the same edge switch, e.g. edge switch X. In this case, when switch X receives a frame from VM1, since the frame DMAC is the edge switch X's MAC address but the destination IP address is not, edge switch X may use the switch MAC address suffix in the DMAC and the destination IP address to perform a lookup in the forwarding table (e.g., similar to FDB 2372) of edge switch X to obtain the DMAC and VLAN ID of VM2 and hence forward the frame to VM2.

In the MAC delegation schemes above, the host MAC address may be unique but the host IP address may not be unique. In a network environment where the host IP address may also be unique, the above MAC delegation schemes may be substantially simplified. In such scenarios, only one MAC address may be required per edge switch and the customer ID may not be needed in the ARP processing scheme since the IP address may uniquely identify a VM. Thus, only the target IP address may be used in the frame forwarding at egress switches and the switch MAC address suffix may not be needed for this purpose. In the data frame forwarding scheme 2800, no additional table lookup may be required to obtain the switch MAC address x₀ when the edge switch may have only one MAC address. The MAC address mapping methods described in references [4] and [5] above may be a special case of the MAC address delegation scheme above by assigning one switch MAC address for each VM MAC address.

In the schemes above, the network wide IP address uniqueness may be relaxed to the edge switch wide IP address uniqueness (or to an edge switch pair if redundancy is required). As such, if multiple VMs connected to the same edge switch (or edge switch pair) each has a unique IP address, a single MAC address may be used for the edge switch. In the data frame forwarding schemes 2700 and 2800, the switch MAC address suffix in the DMAC and the destination IP address may be used at egress switch Z to lookup the forwarding table to obtain the DMAC and VLAN ID of VM2. This applies when some VMs connected to edge switch Z may have a duplicated IP address and may also use the same VLAN ID (e.g., two VMs on two different physical servers may have the same IP address and use the same VLAN ID). In the case where multiple VMs with a duplicated IP address and connected to the same edge switch use different VLAN IDs, and the VMs belonging to the same customer use the same VLAN, one MAC address may be used for an edge switch. In this case, the VLAN ID carried in the frame and the destination IP address may be used in looking up the forwarding table to obtain the DMAC and VLAN ID of VM2.

FIG. 29 illustrates an embodiment of a node failure handling scheme 2900 that may be used in the MAC address delegation scheme. In the node failure handling scheme 2900, a first edge switch 2922 (edge switch X) and a second edge switch 2922 (edge switch Y) may be a protection pair, where one edge switch may be used instead of the other if the other fails. For instance, any VM 2926 (VM1) connected to edge switch X during normal operation may switch over to edge switch Y when edge switch X fails. The switchover may be performed by a virtual edge switch and not VM. Further, a LS 2940 may have the information about edge switches X and Y as a protection pair, which may be obtained using common server rack wiring practices.

When the LS 2940 is notified by the network that edge switch X has failed, the LS 2940 may send the information of the affected VMs (that may be connected to edge switch X) to edge switch Y. The information about each affected VM may include: IP address, MAC address, VLAN ID, customer ID, and switch MAC address (e.g., x₀) (step 1 in FIG. 29). The LS 2940 may also informs all the edge switches 2922 (e.g., including edge switch Z) in the network to forward frames that are destined to edge switch X to edge switch Y instead (step 2 in FIG. 29). Each of the edge switches 2922 (e.g., edge switch Z) may then replace the MAC prefix of edge switch X with the MAC prefix of edge switch Y in its forwarding process.

For instance, for a frame sent from VM2 to VM1, the DMAC may be x₀=02-11-11-11-00-00. As such, edge switch Z may use 02-22-22-22, which may be the MAC prefix of edge switch Y in its forwarding table lookup and change the frame DMAC to 02-22-22-22-00-00 before forwarding the frame to the next hop. Upon receiving the notification of affected VMs (connected to edge switch x including VM1), edge switch Y may perform the following (using VM1 as an example):

a) If edge switch Y knows the switch port to reach VM1, go to c); otherwise b) Edge switch Y may send an ARP request to VM1 (step 3 in FIG. 29). When edge switch Y receives back an ARP reply from VM1, edge switch Y may check VM1's MAC address with the MAC address received from the LS 2940. If the addresses do not match, edge switch Y may send an error message to the LS 2940 and stop; otherwise c) Edge switch Y may update its ARP table, its FDB, and the switch forwarding table for VM1. Specifically, edge switch Y may add a new entry in its FDB and the forwarding table (in the downstream direction) with the suffix of x₀ which may be 00-00 for VM1. d) If using the data frame forwarding scheme 2800, edge switch Y may add a new entry for VM1 to the SMAC mapping table with x₀. Thus, the SMAC of frame from VM1 may be changed to x₀ by the edge switch Y before sending the frame out. Edge switch Y may then resume the role of edge switch X and from the viewpoint of the VMs (connected to edge switche pair X and Y), nothing may be changed regarding frame forwarding. e) Edge switch Y may inform the LS 2940 that the switchover of the affected VMs is completed (step 4 in FIG. 29).

During the above process, edge switch Y may receive frames destined to VM1 and/or from VM1. If edge switch Y receives a frame destined to VM1, edge switch Y may use the suffix of DMAC and the destination IP address to obtain the MAC address of VM1 and the outgoing port ID. If no entry is found, the frame may be discarded. Edge switch Y may send an ARP request to VM1 if edge switch Y has not done so. If edge switch Y receives a frame from VM1, edge switch Y may use the prefix of DMAC to forward the frame, which may applicable to the data frame forwarding scheme 2700. For the data frame forwarding scheme 2800, the SMAC may need to be changed to a MAC address of edge switch Y. If no such address exists, the frame may be discarded. In the data frame forwarding scheme 2700, traffic from VM1 to VM2 may not be interrupted.

Subsequently, the affected VMs (e.g., VM1) may fall back or switch over from edge switch Y to edge switch X when edge switch X may become operational again. In this case, edge switch X may first obtain the affected VMs' information from the LS 2940. The LS 2940 may also inform all the edge switches 2922 to resume the normal operation (for sending frames to the VMs connected to edge switch X). Specifically, frames destined to edge switch X may again be forwarded to edge switch X. The above failure switchover and fallback may also be achieved in a distributed manner if the VM information of edge switch X is also stored in edge switch Y (e.g., sent from edge switch X or the LS 2940 to edge switch Y) and all the edge switches 2922 know that the edge switches X and Y are a redundant pair. Further, if only one MAC address is used per edge switch, the above operation on the MAC address suffix may be omitted.

FIG. 30 illustrates an embodiment of a link failure handling scheme 3000 that may be used in the MAC address delegation scheme. As in the node failure handling scheme 2900, in the link failure handling scheme 3000, a first edge switch 3022 (edge switch X) and a second edge switch 3022 (edge switch Y) may be a protection pair. As such, any VM 3026 (VM1) connected to edge switch X during normal operation may switch over to edge switch Y when edge switch X becomes unreachable, e.g., due to a failure of the path between a virtual switch up link port of VM1 and edge switch X. The switchover may be performed by a virtual edge switch and not VM. Further, a LS 3040 may have the information about edge switches X and Y as a protection pair, which may be obtained using common server rack wiring practices.

When the link fails, edge switch X may inform the LS 3040 of the set of VMs affected by the link failure. The LS 3040 then sends the information of the affected VMs to edge switch Y. Upon receiving the information, edge switch Y may perform the following (using VM1 as an example):

a) If edge switch Y knows the switch port to reach VM1, go to c); otherwise b) Edge switch Y may send an ARP request to VM1 (step 3 in FIG. 30). When edge switch Y receives back an ARP reply from VM1, edge switch Y may check VM1's MAC address with the MAC address received from the LS 3040. If the addresses do not match, edge switch Y may send an error message to the LS 3040 and stop; otherwise c) Edge switch Y may assign a new switch MAC address (e.g., y₀) to VM1 and update its ARP table, its FDB, and the switch forwarding table for VM1. Edge switch Y may also register VM1 to the LS 3040 with the new location information (step 4 in FIG. 30).

In the link failure handling scheme 30, there may be several ways to inform other VMs in the network about the new location of the affected VMs. In a first scheme, edge switch Y may send out a gratuitous ARP message on behalf of VM1 to all the (edge) switches in the network via a pre-established distribution tree. An edge switch 3022 that receives the gratuitous ARP may in turn send the gratuitous ARP message to its attached VMs. This approach may work well if IP addresses are unique within the network or if all the VMs of a customer use one VLAN. In a second scheme, the LS 3040 may send a broadcast message to all the (edge) switches in the network about the new location of VM1. The information may include: IP address, MAC address, customer ID, and new switch MAC address (e.g., y₀). Each edge switch 3022 may then decide whether to send a gratuitous ARP message to a VM attached to it, based on the local information (e.g., ARP table) and the information in the LS message. For instance, an edge switch may decide to send a gratuitous ARP message to the VMs that have the same customer ID as VM1. In a third implementation, the LS 3040 may inform edge switch X to redirect frames destined to VM1 to a MAC address of edge switch Y, e.g., y₀. Thus, the DMAC of redirected frames may be y₀. If the data frame forwarding scheme 2800 is used, edge switch X may also send an ARP reply on behalf of edge switch Y to the senders of the redirected frames to inform them of the new location of VM1. Otherwise, the senders of the redirected frames may send frames directly to edge switch Y after their ARP tables expire and after obtaining the new location of VM1 from the LS 3040.

Similar to the node failure handling scheme 2900, in the link failure handling scheme 3000, edge switch Y may receive frames from VM1 during the above process. If edge switch Y finds that the frame SMAC in the frames is unknown, edge switch Y may discard the frames and start the VM registration scheme 2300. Hence when edge switch Y receives the notification from the LS 3040 about VM1, edge switch Y may continue with rest of the process described above (e.g., inform the other VMs about the VM's new location). Some of the above steps in the link failure handling scheme 3000 may also be used for the case of VM migration. For instance, when a VM migrates from edge switch X or any other edge switch to edge switch Y, the VM may first send a gratuitous ARP message. Upon receiving the gratuitous ARP message, edge switch Y may detect that the VM is a new VM and hence start the VM registration scheme 2300 process and inform the other VMs in the network about the VM's new location as described above.

The MAC address delegation schemes above and the related processes are described for DC environment that comprise VMs, edge switches or TORs, and cores switches. However, the same schemes may be used in other Ethernet-based large L2 network environments to handle duplicated IP addresses and assign one or more MAC addresses, which may be used as delegates for the MAC addresses of hosts connected to a switch or gateway. For instance, the MAC address delegation schemes may be used in a bridged Layer 2 network, such as in the interconnected network districts 1700 or 1800 to delegate multiple MAC addresses to a DBB and thus handle duplicated IP addresses of multiple end stations, servers, or VMs connected to the DBB. The VM registration, ARP processing, data frame forwarding, and/or node/link failure handling schemes above for DCs may also be used in the bridged Layer 2 network environment.

With server virtualization, a physical server may host more VMs, e.g., tens to hundreds of virtual end-stations or VMs. This may result in a substantial increase in the number of virtual hosts in a DC. For example, for a relatively large DC with about 50,000 severs, which may each support up to about 128 VMs, the total number of VMs in the DC may be equal to about 50,000×128 or about 6,400,000 VMs. To achieve dynamic allocation of resources across such large server pool, Ethernet-based Layer 2 networks may be used in DCs. Such a large Layer 2 network with potentially a substantial number of virtual hosts may pose new challenges to the underlying Ethernet technology. For instance, one issue may be MAC forwarding table scalability due to the flat MAC address space. Another issue may be handling a broadcast storm caused by ARP and other broadcast traffic.

One approach to reduce the size of the MAC forwarding table, also referred to herein as a FDB, in the core of the network may be using network address encapsulation, e.g., according to IEEE 802.1ah and TRILL. The network address encapsulations of 802.1ah and TRILL are described in IEEE P802.1ah/D4.2 standard and IETF draft draft-ietf-trill-rbridge-protol-12-txt, respectively, both of which are incorporated herein by reference. With network address encapsulation, the number of FDB entries in core switches may be reduced to the total number of switches (including edge and core) in the network, independent of the number of VMs. For example, with about 20 servers per edge switch, the number of edge switches in a network of about 50,000 servers may be equal to about 50,000/20 or about 2,500. However, with data path MAC address learning, the FDB size of edge switches (e.g., ToR switches in DCs) may be about the same as when network address encapsulation is not used, which may be substantially large.

Even with selective MAC learning at ToR switches, the FDB size may still be substantially large. For example, if a ToR switch has about 40 downstream ports, a pair of ToR switches may have up to about 40 dual-homed servers connected to the ToR switches. If a server supports up to about 128 VMs, a ToR switch may have about 128×40/2 or about 2,560 VMs connected to the ToR switch in normal operation, e.g., when the TOR switches handle about the same number of VMs. The number of VMs may increase to about 5,120 if one ToR switch fails. If each VM communicates on average with about 10 remote VMs simultaneously, the ToR switch FDB size (e.g., number of entries) may be at least proportional to about 2,560 (local VMs)+2,560×10 (remote VMs)+2,500 (ToR switches) or about 30,660 entries, which may be further doubled in the failure scenario.

The network address encapsulations in 802.1ah and TRILL may be symmetric. Specifically, the same switches, such as edge switches, may perform the address encapsulation. The problem with the symmetric network address encapsulations in 802.1ah and TRIL is that an edge switch needs to keep track of the remote VMs that communicate with local VMs. The number of the remote VMs may vary substantially. One solution proposed in reference [1] above is to move the network address encapsulation procedure inside the VMs, thus reducing the switch FDB size to its minimum, which may be equal to the sum of the number of local VMs and the number of edge switches in the network (e.g., equal to about 2,560+2,500 or about 5,060 entries in the above example). A drawback of this approach is the change of guest operation system (OS) protocol stack.

Instead, moving the network address encapsulation to a virtual switch of a physical server (e.g., inside a hypervisor) may reduce the edge switch FDB size and avoid changing the guest OS protocol stack, as described further below. Such a network address encapsulation is referred to herein as asymmetric network address encapsulation since address decapsulation is still done elsewhere in edge switches. This mechanism of asymmetric network address encapsulation may reduce the amount of addresses maintained in the FDBs of intermediate/edge switches or routers.

The asymmetric network address encapsulation scheme may be implemented in a Layer 2 network that comprises edge and core switches, such as in the different network embodiments described above. For instance, the edge switches may correspond to ToR switches in DCs. Each edge switch may be assigned a unique ID, which may be a MAC address (as in 802.1ah), an about 16 bit nickname (as in TRILL), or an IP address. The network may be configured to forward a frame based on the destination edge switch ID carried in the header of the frame from an ingress edge switch to the egress edge switch. The frame may be forwarded inside the network using any transport technology. The asymmetric network address encapsulation scheme may be similar to the address encapsulation scheme in 802.1ah, also referred as MAC-in-MAC. MAC learning may be disabled in the network but enabled on the edge switch server facing ports. The terms server, end-station, and host may be used interchangeably herein. The terms virtual server, VM, virtual end-station, and virtual host may also be used interchangeably herein.

In MAC-in-MAC, there are two types of MAC addresses: the MAC addresses assigned to edge switches, also referred to as network addresses or backbone MAC (B-MAC) addresses, and the MAC addresses used by VMs, also referred to as customer MAC (C-MAC) addresses. FIG. 31 illustrates an embodiment of a typical physical server 3100, which may be a dual-homed server in a DC. The physical server 3100 may comprise a virtual switch 3110, a plurality of VMs 3140, and a plurality of physical network interface cards (pNICs) 3150. The virtual switch 3110 may comprise an ARP proxy 3130 and a FDB 3120, which may comprise a local FDB 3122 and a remote FDB 3124. The virtual switch 3110 may be located inside a hypervisor of the physical server 3100. The virtual switch 3110 may be connected to the VMs via a plurality of corresponding vNICs 3142 of the VMs 3140 and a plurality of corresponding virtual switch ports 3112 of the virtual switch 3110. The virtual switch 3110 may also be connected to the pNICs 3150 via a plurality of corresponding virtual switch trunk ports 3114 of the virtual switch 3110. The pNICs 3150 may serve as uplinks or trunks for the virtual switch 3110. The physical server 3100 may be connected to a plurality of edge switches 3160 via corresponding pNICs 3150 of the physical server 3100. Thus, the edge switches 3160 may be connected via the components of the physical server 3100 (the pNICs 3150 and the virtual switch 3110) to the VMs 3140. The components of the physical server 3100 may be arranged as shown in FIG. 31.

For load balancing, traffic may be distributed to the trunks (pNICs 3150) based on the virtual port IDs or VM source C-MAC addresses of the traffic. Each VM 3140 may have a vNIC 3142 with a uniquely assigned C-MAC address. A VM 3140 may send traffic to an edge switch 3160 during normal operation. For example, a first VM 3140 (VM1) may send a plurality of frames intended to external VMs in other physical servers in the network (not shown) via a corresponding first edge switch 3150 (edge switch X). A second edge switch 3160 (edge switch R) may be a backup for edge switch X. When edge switch X becomes unreachable due to a failure (e.g., the corresponding pNIC 3150 fails, the link between the pNIC 3150 and edge switch X fails, or edge switch X fails), the virtual switch 3110 may then send the frames to edge switch R.

In the FDB 3120, the local FDB 3122 may correspond to the local VMs (VMs 3140) and may comprise a plurality of C-MAC destination addresses (C-MAC DAs), a plurality of VLAN IDs, and a plurality of associated virtual switch port IDs. The C-MAC DAs and VLAN IDs may be used to look up the local FDB 3122 to obtain the corresponding virtual switch port IDs. The remote FDB 3124 may correspond to external VMs (in other physical servers) and may comprise a plurality of B-MAC destination addresses (B-MAC DAs) and a plurality of C-MAC DAs associated with the B-MAC DAs. The C-MAC DAs may be used to look up the remote FDB 3124 by the local VMs to obtain the corresponding B-MAC DAs. The remote FDB 3124 may be populated by the ARP proxy 3130, as described below.

Based on the symmetric address encapsulation, an Ethernet frame from a VM 3140 may be untagged or tagged. If the frame is untagged, the VLAN ID assigned to the corresponding virtual switch port 3112 may be used. In the upstream direction from the VM 3140 to an edge switch 3160, the virtual switch 3110 may perform the following steps after receiving an Ethernet frame from the VM 3140:

Step 1: Use C-MAC DA and VLAN ID in the table lookup of the local FDB 3122. If a match is found, forward the frame to the virtual switch port 3112 that is specified in the matched FDB entry (by the virtual switch port ID). Else, go to step 2.

Step 2: Use C-MAC DA in the table lookup of the remote FDB 3124. If a match is found, perform a MAC-in-MAC encapsulation based asymmetric network address encapsulation (described below) and forward the frame to the virtual switch trunk port 3114 that is associated with the C-MAC SA in the frame. Else, go to step 3.

Step 3: Discard the frame and send an enhanced ARP request to an ARP server in the network (not shown).

FIG. 32 illustrates an embodiment of an asymmetric network address encapsulation scheme 3200 that may be used in the physical server. Based on the asymmetric network address encapsulation scheme 3200, a VM 3202 may send, in the upstream direction, a frame intended to another external or remote VM in another physical server in the network (not shown). The frame may comprise a C-MAC DA (B) 3210 of the remote VM, a C-MAC SA (A) 3212 of the VM 3202, a C-VLAN ID 3214 for the VLAN of the VM 3202, data or payload 3216, and a Frame Check Sequence (FCS) 3218. The VM 3202 may send the frame to a virtual switch 3204.

The virtual switch 3204 (in the same physical server) may receive the frame from the VM 3202. The virtual switch 3204 may process the frame and add a header to the frame to obtain a MAC-in-MAC frame. The header may comprise a B-MAC DA (Y) 3220, a B-MAC SA (0) 3222, a B-VLAN ID 3224, and an Instance Service ID (I-SID) 3226. The B-MAC address (Y) may be associated with the C-MAC DA (B) 3210 in an edge switch 3206. The B-MAC address(Y) may indicate the location of the remote VM that has the C-MAC address (B). The B-MAC SA 3222 may be set to zero by the virtual switch 3204. The B-VLAN ID 3224 may be set to the C-VLAN ID 3214. The I-SID 3226 may be optional and may not be used in the header if the Ethernet frame is only sent to the C-MAC DA (B). The virtual switch 3204 may then send the MAC-in-MAC frame to the edge switch 3206.

The edge switch 3206 (connected to the physical server) may receive the MAC-in-MAC frame from the virtual switch 3204. The edge switch 3206 may process the header of the MAC-in-MAC frame to obtain a new header in the MAC-in-MAC frame. The new header may comprise a B-MAC DA (Y) 3240, a B-MAC SA (X) 3242, a B-VLAN ID 3244, and an I-SID 3246. The B-MAC SA (X) 3242 may be set to the B-MAC address (X) of the edge switch 3206. The B-VLAN ID 3244 may be changed if necessary to match a VLAN in the network. The remaining fields of the header may not be changed. The edge switch 3206 may then forward the new MAC-in-MAC frame based on the B-MAC DA (Y) 3242 and possibly the B-VAN ID 3244 via the network core 3208, e.g., a core network or a network core district.

In the downstream direction, the edge switch 3206 may receive a MAC-in-MAC frame from the network core 3208 and perform a frame decapsulation. The MAC-in-MAC frame may comprise a header and an original frame sent from the remote VM to the VM 3202. The header may comprise a B-MAC DA (X) 3260 for the edge switch 3206, a B-MAC SA (Y) 3262 that corresponds to remote VM and the edge switch 3206, a B-VLAN ID 3264 of the VLAN of the remote VM, and an I-SID 3266. The original frame for the remote VM may comprise a C-MAC DA (A) 3270 for the VM 3202, a C-MAC SA (B) 3272 of the remote VM, a C-VLAN ID 3274 associated with the VM 3202, data or payload 3276, and a FCS 3278. The edge switch 3206 may remove the header from the MAC-in-MAC frame and forward the remaining original frame to the virtual switch 3204. The edge switch 3206 may look up its forwarding table using C-MAC DA (A) 3270 and C-VLAN ID 3274 to get an outgoing switch port ID and forward the original frame out on the physical server facing or connected to the corresponding switch port. In turn, the virtual switch 3204 may forward the original frame to the VM 3202. The virtual switch 3204 may forward the original frame to the VM 3202 based on the C-MAC DA (A) 3270 and the C-VLAN ID 3274.

The forwarding tables in the edge switch 3206 may include a local FDB and a remote FDB. The local FDB may be used for forwarding frames for local VMs and may be populated via MAC learning and indexed by the C-MAC DA and C-VLAN ID in the received frame. The remote FDB may be used for forwarding frames to remote VMs and may be populated by a routing protocol or a centralized control/management plane and indexed by the B-MAC DA and possibly the B-VLAN ID in the received frame.

In the asymmetric address encapsulation scheme 3200, the MAC-in-MAC encapsulation may be performed at the virtual switch 3204, while the MAC-in-MAC de-capsulation may be performed at the edge switch 3206. As such, the FDB size in the edge switches may be substantially reduced and become more manageable even for a substantially large Layer 2 network, e.g., in a mega DC. The remote FDB size in the virtual switch 3204 may depend on the number of remote VMs in communication with the local VMs, e.g., the VM 3202. For example, if a virtual switch supports about 128 local VMs and each local VM on average communicates with about 10 remote VMs concurrently, the remote FDB may comprise about 128×10 or about 1,289 entries.

FIG. 33 illustrates an embodiment of an ARP processing scheme 3300 that may be used in the physical server 3100. Based on the ARP processing scheme 3300, a VM 3302 may broadcast an ARP request for a remote VM. The ARP request may comprise a C-MAC DA (BC) 3310 that indicates a broadcast message, a C-MAC SA (A) 3312 of the VM 3302, a C-VLAN ID 3314 for the VLAN of the VM 3302, ARP payload 3316, and a FCS 3318.

A virtual switch 3304 (in the same physical server), which may be configured to intercept all ARP messages from local VMs, may intercept the ARP request for a remote VM. An ARP proxy in the virtual switch 3304 may process the ARP request and add a header to the frame to obtain a unicast extended ARP (ERAP) message. The frame may be encapsulated using MAC-in-MAC, e.g., similar to the asymmetric network address encapsulation scheme 3200. The header may comprise a B-MAC DA 3320, a B-MAC SA (0) 3322, a B-VLAN ID 3324, and an I-SID 3326. The B-MAC DA 3320 may be associated with an ARP server 3308 in the network. The B-VLAN ID 3324 may be set to the C-VLAN ID 3314. The I-SID 3326 may be optional and may not be used. The EARP message may also comprise a C-MAC DA (Z) 3328, a C-MAC SA (A) 3330, a C-VLAN ID 3332, an EARP payload 3334, and a FCS 3336. The ARP proxy may replace the C-MAC DA (BC) 3310 and the ARP payload 3316 in the received frame with the C-MAC DA (Z) 3328 for the remote VM and the EARP payload 3334, respectively, in the EARP message. The virtual switch 3304 may then send the EARP message to the edge switch 3306.

The edge switch 3306 may process the header in the EARP message to obtain a new header. The new header may comprise a B-MAC DA (Y) 3340, a B-MAC SA (X) 3342, a B-VLAN ID 3344, and an I-SID 3346. The B-MAC SA (X) 3342 may be set to the B-MAC address (X) of the edge switch 3306. The B-VLAN ID 3344 may be changed if necessary to match a VLAN in the network. The remaining fields of the header may not be changed. The edge switch 3306 may then forward the new EARP message to the ARP server 3308 in the network.

The ARP server 3308 may process the received EARP message and return an EARP reply to the edge switch 3306. The EARP reply may comprise a header and an ARP frame. The header may comprise a B-MC DA (X) 3360 for the edge switch 3306, a B-MAS SA 3362 of the ARP server 3308, a B-VLAN ID 3364, and an I-SID 3366. The ARP frame may comprise a C-MAC DA (A) 3368 for the VM 3302, a C-MAC SA (Z) 3370 for the requested remote VM, a C-VLAN ID 3372, an EARP payload 3374, and a FCS 3376. The edge switch 3306 may decapsulate the EARP message by removing the header and then forward the ARP frame to the virtual switch 3304. The virtual switch 3304 may process the ARP frame and send an ARP reply accordingly to the VM 3302. The ARP reply may comprise a C-MAC DA (A) 3390 for the VM 3302, a C-MAC SA (B) 3392 associated with remote VM's location, a C-VLAN ID 3394, an ARP payload 3396, and a FCS 3398.

The ARP proxy in the virtual switch 3304 may also use the EARP message to populate the remote FDB in the edge switch 2506. The ARP proxy may populate an entry in the FDB table with a remote C-MAC and remote switch B-MAC pair, which may be found in the EARP payload 3374. The C-MAC and remote switch B-MAC may be found in a SHA field and a sender location address (SLA) field, respectively, in the EARP payload 3374.

A hypervisor in the physical server that comprises the virtual switch 3304 may also register a VM, e.g., the local VM 3302 or a remote VM, with the ARP server 3308 in a similar manner of the ARP processing scheme 3300. In this case, the virtual switch 3304 may send a unicast EARP frame to the ARP server 3308 with all the sender fields equal to all the target fields. Another way to register the VM is described in U.S. Provisional Patent Application No. 61/389,747 by Y. Xiong et al. entitled “A MAC Address Delegation Scheme for Scalable Ethernet Networks with Duplicated Host IP Addresses,” which is incorporated herein by reference as if reproduced in its entirety. This scheme may handle the duplicated IP address scenario.

FIG. 34 illustrates an embodiment of an EARP payload 3400 that may be used in the ARP processing scheme 3300, such as the EARP payload 3374. The EARP payload 3400 may comprise a hardware type (HTYPE) 3410, a protocol type (PTYPE) 3412, a hardware address length (HLEN) 3414, a protocol address length (PLEN) 3416, an operation field (OPER) 3418, a SHA 3420, a SPA 3422, a target hardware address (THA) 3424, and a target protocol address (TPA) 3426, which may be elements of a typical ARP message. Additionally, the EARP payload 3400 may comprise a SLA 3428 and a target location address (TLA) 3430. FIG. 6 also shows the bit offset for each field in the EARP payload 3400, which also indicates the size of each field in bits.

One issue with using the ARP server (e.g., the ARP server 3308) and disabling MAC learning in the network is the case where a VM becomes unreachable due to a failure of its edge switch or the link connecting the ARP server to the edge switch. In this case, it may take some time for the virtual switch to know the new location of a new or replacement edge switch for the VM. For example, if the edge switch X in the physical server 3100 becomes unreachable, the virtual switch 3110 may forward frames from VM1 to the edge switch R, which may become the new location for VM1.

To reduce the time for updating the remote FDB in a virtual switch 3110 about the new location of a VM, a gratuitous EARP message may be used. The virtual switch 3110 may first send a gratuitous EARP message to the edge switch R in a MAC-in-MAC encapsulation frame, including a B-MAC DA set to broadcast address (BC). In the gratuitous EARP message, the SHA (e.g., SHA 3420) may be set equal to the THA (e.g., THA 3424), the SPA (e.g., SPA 3422) may be set equal to the TPA (e.g., TPA 3426), and the SLA (e.g., SLA 3428) may be set equal to TLA (e.g., TLA 3430). The edge switch R may then send the gratuitous EARP message to a plurality of or to all other edge switches in the network, e.g., via a distribution tree. When an edge switch receives the gratuitous EARP message, the edge switch may decapsulate the message and send the message out on the edge switch's server facing ports. When a virtual switch then receives the gratuitous EARP message, the virtual switch may update its remote FDB if the SHA already exists in the remote FDB. The ARP server in the network may update the new location of the affected VM in the same way.

The asymmetric network address encapsulation scheme described above may use the MAC-in-MAC encapsulation in one embodiment. Alternatively, this scheme may be extended to other encapsulation methods. If TRILL is supported and used in a network, where an edge switch is identified by an about 16 bit nickname, the TRILL encapsulation may be used in the asymmetric network address encapsulation scheme. Alternatively, an IP-in-IP encapsulation may be used if an edge switch is identified by an IP address. Further, network address encapsulation may be performed at the virtual switch level and the network address de-capsulation may be performed at the edge switch level. In general, the network address encapsulation scheme may be applied at any level or any of the network components as long as the encapsulation and de-capsulation are kept at different levels or components.

In a bridged network that is partitioned into districts, such as in the interconnected network districts 1800, a DBB may be a bridge participating in multiple districts. The DBB's address may be referred to herein as a network address to differentiate the DBB's address from the C-MAC addresses of the VMs in each district. Using the asymmetric address encapsulation scheme above, the encapsulation of the network address may be performed at the switch closer to hosts or the virtual switch closer to virtual hosts. For example, the intermediate switches 1824, e.g., ToR switches, may perform the network address encapsulation. The intermediate switches 1824 may encapsulate the data frames coming from the subsets of hosts and that comprise a target DBB address. However, the intermediate switches 1824 may not alter data frames incoming from the network side, e.g., the DBBs 1822 in the core district 1810. The target DBB 1822, which is one level above the intermediate switch 1824, may decapsulate the data frames from network side (core district 1810) and forward the decapsulated data frame towards hosts within its district.

In an embodiment, a virtual switch insider a physical server (e.g., an end-station 1826) may perform the network address encapsulation, while the target DBB 1822 may perform the network address decapsulation. In this case, the DBB 1822 that performs the decapsulation may be two levels above the virtual switch (in the end-station 1826) that performs the encapsulation.

The bridged network connected to the DBB 1822 (e.g., the core district 1810) may be IP based. The core network (or district) that interconnects the DBBs may be a L3 Virtual Private Network (VPN), a L2 VPN, or standard IP networks. In such scenarios, the DBB may encapsulate the MAC data frames from its local district with a proper target DBB address, which may be an IP or MPLS header.

FIG. 35 illustrates an embodiment of a data frame forwarding scheme 3500 that may be used in a Layer 2 bridged network, such as for the interconnected network districts 1800. The data frame forwarding scheme 3500 may also implement the asymmetric network address encapsulation scheme above. The Layer 2 bridged network may comprise a core district 3510, a plurality of DBBs 3522 or district boundary switches in a plurality of districts 3520 connected to the core district 3510, and a plurality of intermediate or edge switches 3524 and physical servers 3526 connected to corresponding DBBs 2022 in their districts 3520. The physical servers 3526 may comprise a plurality of VMs and virtual switches (not shown). Some of the DBBs 3522, intermediate/edge switches 3524, and physical servers 3526 across the districts 3520 may belong to a VLAN established in the Layer 2 bridged network and associated with a VLAN ID. The components of the Layer 2 bridged network may be arranged as shown in FIG. 35.

According to the asymmetric network address encapsulation scheme, an intermediate/edge switch 3524 may receive a frame 3540, e.g., an Ethernet frame, from a first VM (host A) in a physical server 3526 in a first district (district 1). The frame 2040 may be intended for a second VM (host B) in a second physical server 3526 in a second district (district 2). The frame 2040 may comprise a B-MAC DA 3542 for a second DBB (DBB2) in district 2, a B-MAC SA 3544 for host A (ToR A), a C-MAC DA 3546 for host B (B), a C-MAC SA 3548 for host A (A), an IP-SA 3550 for host A (A), an IP-DA 3552 for host B (B), and payload. The intermediate/edge switch 3524 may forward the frame 2040 to a first DBB 3522 (DBB1) in district 1. DBB1 may receive and process the frame 3540 to obtain an inner frame 3560. The inner frame 3560 may comprise a B-MAC DA 3562 for DBB2, a B-MAC SA 3564 for DBB1, a C-MAC DA 3566 for host B (B), a C-MAC SA 3568 for host A (A), an IP-SA 3570 for host A (A), an IP-DA 3552 for host B (B), and payload. DBB1 may then forward the inner frame 3560 to district 2 via the core district 3510.

DBB2 in district 2 may receive and decapsulate the inner frame 3540 to obtain a second frame 3580. DBB2 may remove B-MAC DA 3562 for DBB2 and a B-MAC SA 3564 from the inner frame 3560 to obtain the second frame 3580. Thus, the second frame 3580 may comprise a C-MAC DA 3582 for host B (B), a C-MAC SA 3584 for host A (A), an IP-SA 3586 for host A (A), an IP-DA 3588 for host B (B), and payload. DBB2 may send the second frame 3580 to host B in district 2.

In the data frame forwarding scheme 3500, the intermediate/edge switch 3524 may not perform the MAC-in-MAC function for frames received from local physical servers 3524 connected to the intermediate/edge switch 3524. In another embodiment, the encapsulation procedure of the first frame 3540 may be performed by a virtual switch in the physical server 3526 instead of the intermediate/edge switch 3524, which may forward the first frame 3540 without processing from the physical server 3526 to the corresponding DBB 3522.

FIG. 36 illustrates an embodiment of an enhanced ARP processing method 3600 that may be used in a Layer 2 bridged network, such as for the interconnected network districts 1800. The enhanced ARP processing method 3600 may begin at step 3601, where a local host 3610 may send an ARP request to a local location 3630 via a first bridge 3620, e.g., a local DBB. The local location 3630 may correspond to the same location or district as the local host 3610. The ARP request may be sent to obtain a MAC address associated with a remote host 3660. The local host 3610 may be assigned an IP address IPA and a MAC address A. The remote host 3660 may be assigned an IP address IPB and a MAC address B. The ARP request may comprise a SA MAC address A and A SA IP address IPA for the local host 3610. The ARP request may also comprise a DA MAC address set to zero and a DA IP address IPB for the remote host 3660. The local location 3630 may forward the ARP request to an ARP server 3640 in the network.

At step 3602, the ARP server 3640 may send an EARP response to the first bridge 3620. The EARP response may comprise a SA MAC address A and a SA IP address IPA for the local host 3610, a DA MAC address B and a DA IP address IPB for the remote host 3660, and a MAC address for a second bridge in a remote location 3650 of the remote host 3660. At step 3603, the first bridge 3620 may process/decapsulate the EARP response and send an ARP response to the local host 3610. The ARP response may comprise the MAC address A and IP address IPA for the local host 3610, and the MAC address B and the IP address IPB for the remote host 3660. Thus, the local host 3610 may become aware of the MAC address B of the remote host 3660. The first bridge 3620 may also associate (in a local table) the MAC address Y of the remote bridge in the remote location 3650 with the IP address IPB of the remote host 3660. The first bridge 3620 may not need to store the MAC address B of the remote host 3660.

At step 3604, the local host 3610 may send a data frame intended for the remote host 3660 to the first bridge 3620. The data frame may comprise a SA MAC address and SA IP address of the local host 3610, and the DA MAC address and DA IP address of the remote host 3660. At step 3605, the first bridge 3620 may receive and process/encapsulate the data frame to obtain an inner frame. The inner frame may comprise a SA MAC address X of the first bridge 3620, a DA MAC address Y of the remote bridge, a DA MAC address B and a DA IP address IPB of the remote host 3660, and a SA MAC address A and a SA IP address IPA of the local host 3610. At step 3606, the remote bridge in the remote location 3650 may receive the inner frame and process/decapsulate the inner frame to obtain a second frame by removing the SA MAC address X of the first bridge 3620 and the DA MAC address Y of the remote bridge. Thus, the second frame may be similar to the initial frame sent from the local host 3610. The remote bridge may then send the second frame to the remote host 3660. The method 3600 may then end.

In the enhanced ARP processing method 3600, the core network may use 802.1aq or TRILL for topology discovery. If the core network uses 802.1aq for topology discovery, then the first bridge 3620 may not encapsulate the frame sent form the local host 3610 and may forward the frame to the remote location 3650 without processing. Further, the frame forwarded through the core network may be flooded only in the second location 3650 and only when the outbound port indicated in the frame has not been learned.

In an embodiment, an extended address resolution scheme may be implemented by district gateways or gateway nodes that may be TRILL edge nodes, MAC-in-MAC edge nodes, or any other type of overlay network edge nodes. The extended address resolution scheme may be based on the ARP proxy scheme implemented by a DBB in a plurality of districts in a Layer 2 bridged network, such as the ARP proxy scheme 1900. For example, the intermediate/edge nodes 3524 that may be connected to a plurality of physical servers and/or VMs may implement an extended address resolution scheme similar to the ARP proxy scheme described above. The gateway node may use the DS server in the ARP proxy scheme to resolve mapping between a target destination (e.g., host) and an egress edge node. The egress edge node may be a target district gateway, a TRILL egress node, a MAC-in-MAC edge node, or any other type of overlay network edge node. The reply from the DS may also be an EARP reply as described above.

The extended address resolution scheme may be used to scale DC networks with a substantial number of hosts. The overlay network (e.g., bridged network) may be a MAC-in-MAC, TRILL, or other types of Layer 3 or Layer 2 over Ethernet networks. The overlay network edge may be a network switch, such as an access switch (or ToR switch) or an aggregation switch (or EoR switch). The overlay network edge may also correspond to a virtual switch in a server. There may be two scenarios for overlay networks for using the extended address resolution scheme. The first scenario corresponds to a symmetric scheme, such as for TRILL or MAC-in-MAC networks. In this scenario, the overlay edge node may perform both the encapsulation and decapsulation parts. The second scenario corresponds to an asymmetric scheme, where the overlay network may implement the asymmetric network address encapsulation scheme above.

FIG. 37 illustrates an embodiment of an extended address resolution method 3700 that may be implemented in an overlay network. The extended address resolution method 3700 may begin at step 3701, where a first VM 3710 (VM A) may send a frame or packet addressed for a second VM 3780 (VM B) to a first hypervisor (HV) 3720 (HV A). VM A and VM B may be end hosts in different districts. VM A may be connected to HV A in a first district and VM B may be connected to a second HV 3770 (HV B) in a second district. The HV may be an overlay network node configured to encapsulate or add the overlay network address header on a data frame or packet. In the symmetric scheme scenario, the HV may be a DBB, a TRILL edge node, or a MAC-in-MAC edge node. In the asymmetric scheme scenario, the HV may be a virtual switch within a hypervisor or an access switch.

At step 3702, HV A may send an address resolution (AR) request to an ARP server 3730 to retrieve mapping from VM B IP address to a VM B MAC address and HV B MAC address pair, in the case of the symmetric scheme. The ARP server may comprise or correspond to a DS server, such as the DS 1940. In the asymmetric scheme, the mapping may be from VM B IP address to a VM B MAC address and second DBB 3760 (DBB B) MAC address pair. DBB B may be a remote DBB in the same district of VM B.

HV A may also be configured to intercept (broadcasted) ARP requests from local VMs and forward the ARP requests to the DS server. HV A may then retrieve EARP replies from the DS server and cache the mappings between target addresses and target gateway addresses (as indicated by the EARP replies). The target gateway address may also be referred to herein as a target location address. In another embodiment, instead of intercepting ARP requests by HV A, the DS server may send consolidated mapping information to HV A on regular or periodic basis or when VMs move or migrate between districts. The consolidated mapping information may comprise the same information exchanged with L2GWs in the virtual Layer 2 networks described above. For instance, the consolidated mapping information may be formatted as gratuitous group announcements, as described above.

At step 3703, HV A may create an inner address header that comprise (SA: VM A MAC, DA: VM B MAC) and an outer header that comprises (SA: HV A MAC, DA: HV B MAC), in the case of the symmetric scheme. In the asymmetric scheme, the outer header may comprise (SA: HV A MAC, DA: DBB B MAC). HV A may add the inner header and outer header to the frame received from VM A and send the resulting frame to a bridge 3740 connected to HV A in the same district. Within the district, the DA of the outer header, which may be HV B MAC or DBB B MAC, may not be known.

At step 3704, the frame may be forwarded from the bridge 3740 to a first DBB 3750 (DBB A) in the district. At DBB A, the DA HV B MAC or DBB B MAC may be known since the core may be operating on routed forwarding (e.g., 802.1aq SPBM or TRILL) and learning may be disabled in the core. At step 3705, DBB A may forward the frame to DBB B.

At step 3706, DBB B may forward the frame to HV B since DBB may know all HV addresses from the routing subsystem, in the case of the symmetric scheme. In the asymmetric scheme, DBB may remove the outer header comprising (DA: DBB MAC) and forward the frame to VM B MAC in the remaining header, since addresses local to the district may be registered and known within the district.

At step 3707, HV B may receive the frame, remove the outer header comprising (DA: HV B MAC), and forward the resulting frame to VM B MAC in the remaining header, since addresses local to the server are known to HV B, in the case of the symmetric scheme. Additionally, HV B may learn the mapping from VM A MAC (SA in the remaining header) to HV A MAC (SA in the removed header), which may be subsequently used in reply frames from VM B to VM A. In the asymmetric scheme, in addition to forwarding the frame to VM B, HV B may send an ARP message to the ARP (or DS) server 3730 to retrieve the mapping from VM A MAC (SA in the remaining header) to DBB A MAC, which may be subsequently used in reply frames from VM B to VM A.

VM B may then send frames addressed to VM A (IP destination address). At step 3708, HV B may create an inner address header that comprises (SA: VM B MAC, DA: VM A MAC) and an outer header that comprises (SA: HV B MAC, DA: HV A MAC) to a frame, in the case of the symmetric scheme. HV B may maintain VM A IP to VM A MAC mapping and VM A MAC to HV A MAC mapping from a previously received message or AR response. In the asymmetric scheme, the outer header may comprise (SA: HV B MAC, DA: DBB A MAC). HV B may maintain VM A MAC to DBB A MAC mapping from a previously received AR response. Alternatively, HV B may send an ARP message to the ARP (or DS) server to retrieve the mapping when needed. The frame may then be forwarded from VM B to VM A in the same manner described in the steps above (e.g., in the reverse direction). The method 3700 may then end.

FIG. 38 illustrates an embodiment of a network component unit 3800, which may be any device that sends/receives packets through a network. For instance, the network component unit 3800 may be located at the L2GWs across the different locations/domains in the virtual/pseudo Layer 2 networks. The network component unit 3800 may comprise one or more ingress ports or units 3810 for receiving packets, objects, or TLVs from other network components, logic circuitry 3820 to determine which network components to send the packets to, and one or more egress ports or units 3830 for transmitting frames to the other network components.

The network components described above may be implemented on any general-purpose network component, such as a computer system or network component with sufficient processing power, memory resources, and network throughput capability to handle the necessary workload placed upon it. FIG. 39 illustrates a typical, general-purpose computer system 3900 suitable for implementing one or more embodiments of the components disclosed herein. The general-purpose computer system 3900 includes a processor 3902 (which may be referred to as a CPU) that is in communication with memory devices including second storage 3904, read only memory (ROM) 3906, random access memory (RAM) 3908, input/output (I/O) devices 3910, and network connectivity devices 3912. The processor 3902 may be implemented as one or more CPU chips, or may be part of one or more application specific integrated circuits (ASICs).

The second storage 3904 is typically comprised of one or more disk drives or tape drives and is used for non-volatile storage of data and as an over-flow data storage device if RAM 3908 is not large enough to hold all working data. Second storage 3904 may be used to store programs that are loaded into RAM 3908 when such programs are selected for execution. The ROM 3906 is used to store instructions and perhaps data that are read during program execution. ROM 3906 is a non-volatile memory device that typically has a small memory capacity relative to the larger memory capacity of second storage 3904. The RAM 3908 is used to store volatile data and perhaps to store instructions. Access to both ROM 3906 and RAM 3908 is typically faster than to second storage 3904.

At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R₁, and an upper limit, R_(u), is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 7 percent, . . . , 70 percent, 71 percent, 72 percent, . . . , 97 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present disclosure. The discussion of a reference in the disclosure is not an admission that it is prior art, especially any reference that has a publication date after the priority date of this application. The disclosure of all patents, patent applications, and publications cited in the disclosure are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to the disclosure.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein. 

1. An apparatus comprising: a plurality of district boundary bridges (DBBs) in a plurality of second network districts configured to couple to a plurality of core bridges in a core network district and to a plurality of end-stations in the second network districts via a plurality of intermediate switches in the second network districts; wherein the core bridges and the DBBs are aware of a plurality of Media Access Control (MAC) addresses of the DBBs but are not aware of Internet Protocol (IP) addresses and MAC addresses of the end-stations, and wherein the IP addresses of the end-stations are mapped in a directory service (DS) in the core network district to the MAC addresses of the corresponding DBBs in the corresponding second network districts of the end-stations.
 2. The apparatus of claim 1, wherein at least some of the DBBs, intermediate switches, and end-stations across the second network districts are connected over a Virtual Local Area Network (VLAN) that is assigned a VLAN identifier (VID), and wherein the core network district and the second network districts are part of a Layer 2 network.
 3. The apparatus of claim 2, wherein the DS comprises a DS address table that maps the IP addresses of the end-stations to the MAC addresses of the corresponding DBBs for each VID.
 4. The apparatus of claim 2, wherein the end-stations in the VLAN are separated over a plurality of subnets, and wherein each subnet is associated with a subnet identifier (ID).
 5. The apparatus of claim 4, wherein the IP addresses of the end-stations for each subnet are mapped to a plurality of delegate MAC addresses of the corresponding DBBs in the corresponding second network districts of the end-stations.
 6. The apparatus of claim 5, wherein the DS address table maps the IP addresses of the end-stations to the delegate MAC addresses of the corresponding DBBs for each subnet ID.
 7. The apparatus of claim 4, wherein different subnets comprise a plurality of duplicated IP addresses of the end-stations.
 8. An apparatus comprising: a plurality of edge nodes coupled to a core network; a plurality of hosts coupled to the edge nodes, wherein if multiple hosts coupled to an edge node are assigned the same duplicated address by a plurality of different customers, then the edge node is assigned a plurality of delegate addresses that correspond to the multiple hosts that are assigned the same duplicated address, and wherein the delegate addresses are used by other edge nodes and the core network to forward a plurality of frames from other hosts connected to the other edge nodes to the edge node that uses the delegate addresses to forward the frames properly to the corresponding multiple hosts that connected to the edge node and are assigned the same duplicated address.
 9. The apparatus of claim 8, wherein the duplicated address is an Internet Protocol (IP) address and the delegate addresses are Media Access Control (MAC) addresses.
 10. The apparatus of claim 9, wherein the edge node comprises an Address Resolution Protocol (ARP) proxy that is configured to check if a source MAC address and source IP address pair in a frame received from a host connected to the edge node is found in an ARP table of the edge node and register the host if the source MAC address and source IP address pair is not found before performing ARP processing.
 11. The apparatus of claim 10, wherein the ARP processing comprises assigning a switch MAC address to the host by the edge node and then sending an ARP registration to a location server (LS) that is configured to assign a customer identifier (ID) that corresponds to the host real MAC address and send back the customer ID in an ARP confirmation message to the edge node.
 12. The apparatus of claim 10, wherein the ARP proxy is configured to receive an ARP request from the host, use a MAC or a MAC and an IP address in the ARP request to find a corresponding customer ID in the ARP table, use a target IP address in the ARP request and the customer ID to find a target MAC address in another table, and return the target MAC address to the host in an ARP reply if the target MAC address is found, and if the target MAC address is not found, send a request that includes a target IP address and a customer ID to a location server (LS) to get the target MAC address.
 13. The apparatus of claim 9, wherein the delegate addresses are assigned in a compact manner based on an address prefix, where the first about 4 octets of a MAC address is used as a switch MAC address prefix to indicate the location of the hosts and the last about 2 octets of the MAC address are used as a MAC address suffix to indicate each individual host from the multiple hosts connected to the edge switch and assigned the same duplicated address.
 14. The apparatus of claim 13, wherein the switch MAC address suffix and the IP address of each of the hosts is used to forward a frame at the edge switch to a corresponding host connected to the edge switch.
 15. The apparatus of claim 8, wherein a first edge node and a second edge node from the edge nodes form a protection/redundant pair, wherein if the first edge node or a link between the first edge node and a host fails, then the first edge node informs a location server (LS) of the failure that subsequently notifies the second edge node of the failure and sends information about each affected host that is connected to the first edge node to the second edge node, and wherein if the first edge node fails, the LS also informs other edge nodes to send frames destined to the first edge node to the second edge node by replacing the frames' DMAC prefix with the second edge node's MAC prefix.
 16. The apparatus of claim 8, wherein the core network is located in a data center (DC), the edge nodes are Top-Of-Rack (TOR) switches, and the hosts are virtual machines (VMs).
 17. The apparatus of claim 8, wherein the core network is located in a core district, the edge nodes are district boundary bridges (DBBs), and the hosts are servers.
 18. The apparatus of claim 8, wherein the hosts belong to a single VLAN or belong to a plurality of VLANs, and wherein the edge node does not use a VLAN identifier (ID) to forward the frames properly to the corresponding multiple hosts that are assigned the same duplicated address.
 19. A network component comprising: a receiver configured to receive a plurality of Internet Protocol (IP) addresses and Media Access Control (MAC) addresses for a plurality of hosts in a corresponding district in a bridged Layer 2 network; a logic circuit configured to map the IP addresses of the hosts to a MAC address; and a transmitter configured to announce the MAC address and the IP addresses of the hosts but not the MAC addresses of the hosts to a core district in the bridged Layer 2 network.
 20. The network component of claim 19, wherein the hosts send their IP addresses and MAC addresses via a plurality of gratuitous Address Resolution Protocol (ARP) messages.
 21. The network component of claim 20, wherein a plurality of delegate MAC addresses associated with the same application in the corresponding district are announced for a plurality of subnets in the bridged Layer 2 network, and wherein the delegate MAC addresses are mapped to the same IP address for the application.
 22. The network component of claim 21, wherein a frame received via the core district and that comprises a MAC destination address (DA) equal to one of the delegate MAC addresses and an IP DA equal to the IP address of the application is sent to the application in the corresponding district after translating the delegate MAC DA to a MAC DA corresponding to the IP address of the application that is mapped to the delegate MAC address.
 23. The network component of claim 20, wherein the MAC address and the IP addresses of the hosts are announced to the core district via a gratuitous Address Resolution Protocol (ARP) message.
 24. The network component of claim 20, wherein a frame received via the core district and that comprises a MAC destination address (DA) equal to the MAC address and an IP DA of one of the hosts in the corresponding district is sent to the one of the hosts in the corresponding district after translating the MAC DA to a MAC DA corresponding to the IP DA of the one of the hosts that is mapped to the MAC address.
 25. A method comprising: receiving an Address Resolution Protocol (ARP) request from a first end-station in a local district in a bridged Layer 2 network for a Media Access Control (MAC) address associated with a second end-station in a second district in the bridged Layer 2 network; sending a directory service (DS) query to obtain a MAC address associated with the second end-station; receiving a DS response that indicates the MAC address associated with the second end-station; and sending an ARP response that comprises the MAC address associated with the second end-station to the first end-station.
 26. The method of claim 25, wherein the ARP request comprises an Internet Protocol (IP) destination address (DA) of the second end-station and an IP source address (SA) and a MAC SA of the first end-station, and wherein the ARP response comprises an IP DA and a MAC DA of the first end-station, an IP SA of the second end-station, and a MAC address of a district boundary switch associated with the second end-station in the second district.
 27. The method of claim 26, wherein an IP address of the second end-station is associated with the MAC address of the district boundary switch in an ARP table in the first end-station after receiving the ARP response.
 28. The method of claim 26, wherein the DS query comprises an IP address of the second end-station and the IP SA and the MAC SA of the first end-station, and wherein the DS response comprises the IP address of the second end-station and the MAC address of the district boundary switch.
 29. The method of claim 28, wherein the IP address and a MAC address of the second end-station are associated with the MAC address of the district boundary switch in a DS address table in the bridged Layer 2 network.
 30. The method of claim 29, wherein the MAC address of the boundary switch in the DS address table is replaced by a second MAC address for a second boundary district switch that replaces the boundary district switch if the boundary district switch fails.
 31. The method of claim 30, wherein the second district boundary switch is a standby district boundary switch that is added to the same VLAN of the failed district boundary switch, the first end-station, and the second end-station in the bridged layer 2 network. 